Those of you that know me personally know I am very bowlegged. So much so that I can run my fist between my knees without touching when my feet placed tightly together. Over the years this has caused me many performance issues, the worst of which is offside tail kick out. Basically, at an extreme body angle my right rear leg digs into the water and ejects the ski! The shorter the line the worse it got! Eventually I learned to moderate this by better technique, skiing wider tailed skis, rotating my right rear binding, using deeper than normal fin settings and even trying to wrap my knees together. Most of these moves achieved some limited success but I found some of these methods to be ridiculous, uncomfortable, and/or performance limiting at the least, and medically debilitating at worst. As a result of the induced hip pain I now run my bindings dead center front and back. Being a former snow skier and in search of a remedy, I started messing with canting.
Canting a waterski binding is relatively easy thing to do. Initially, I just used plastic washers stacked up with slightly longer screws under the binding plate. I tried one side, then the other. I tried canting the front boot only, both boots, and back boot only on each side. I even tried canting both boots on opposite sides. For me, the best performance increases came from canting the front boot only on my offside. Both boots canted on my offside worked, forced my rear knee inward but also but caused me hip pain. Presently I am running 1/4 inch cant on my offside front boot. I plan on increasing that by 1/8 inch this spring to see if it helps.

Mess around with canting. If it helps, keep it. If not discard it.
Comments
Horton is my hero
@teammalibu I plan to! I do weird science because I am cheap!
@Bruce_Butterfield Many have known that for years! Ask MS!
Absolutely proves us LFF skiers are weird but we solve our problems any way we can.
I like the MOB plate for these needs. For years it was hard for me to get enough wedge as well as cant in my boots/binding.
I can now insert a wedge / cant plate between the boot and the release plate.
I do not recommend any of this sort of thing unless you are bio-mechanically a very hot mess.
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The material is a plastic canted and angled on a belt sander.
I would have disagree with Mr Horton in his assessment of these concepts. Cleaner and more reliable outcome vs sticking beauty washers under one side of the boot plate.
The radar boot platform has potential for all kinds of secondary wedge or cant between either a standard boot plate or a release style like a MOB.
I actually belive wedging is one area of binding /boot to ski technology that has been overlooked or just not explored..
As always, just IMO.
If you live anywhere near a place where snow skiing is popular, take your Vapor boots to the best ski shop you can find. They'll have a device you can stand on with your boots on both feet that will determine the exact wedge angle you need for each leg. If you're an ORT user, take that along, but wear a thin sock with it, out of consideration for the ski tech's delicate sensibilities.
A few things I figured out with washers under one side is that it fatigued the mounting plate at the screw holes and allowed for excessive flex in the foot bed.
Went through a couple binding plates in less then 2 years as they cracked around the screw holes.
Years ago I rode fogman system. I had our machinest at correct craft mill a canted wedge to go under the front boot. Worked great.
I've forgotten the details because I determined I was more of a soft boot guy.
Horton is my hero
I disagree. In my experience very few people have identical cant requirements for each foot, and the only way to determine that accurately is to get independent values for each. At a very minimum, the cant-measuring machine offers a good baseline place to start. In the end, some experimentation on the water will be necessary in any case.
Also, I think you misunderstand how canting works on a water ski. In that regard, you concerns about the cant-measuring machine being different from water skiing is spot on, because with snow skiing your canting effort is designed to make each of your two skis flat under your individual bowed legs. With a water ski, your goal is the opposite - you want to force each of your knees to be aligned over the ski, thereby closing the natural gap between them. So, if you are right foot forward (and bowlegged) you want the thicker edge of the wedge on the right edge of the ski, not under your arch.
Remember the OP's concern about his rear knee dragging in the water on his offside turn? If you place a wedge the way you're describing it you're simply forcing Thager's back knee deeper into the water (on his offside). Instead, you want the wedge to force his knee inward toward the ski's center-line. I know it's counter-intuitive, and you'll probably accuse me of being crazy, but before you do, read this:
https://ballofspray.com/forum#/discussion/15667/canting-my-bindings-on-the-ski-helped-me-overcome-years-of-problems/p1