I'm really impressed by what Precision Blade Honing has to offer. I spent a dozen years figuring out some of what they sell pre-packaged, and some of what they have appears to be better, like you would expect from people with access to a precision machine shop, and the tool-using knowledge that goes with it. Of course, it's all priced for professional skate shops, a bit high for home users. But what a great resource!
Have you tried the hollow sharpening tool that you mentioned? In particular, you once mentioned looking for a hand-tool to create 7/16" hollow. BTW, I'm not sure if ordinary sandpaper would fit their tool. Maybe the sandpaper needs to be a particular thickness.
I've had some thought about adapting the Pro-Filer to work with thinner blades.
Wouldn't your scheme bring you back again to the difficult problem of centering of stuff exactly?
I've dealt with thinner blades by taping the blade, along the edge, with a carefully selected tape. Requires a lot of care to be even, but it can work.
I've tried to tape the Pro-Filer gap itself - but can't figure out a way to apply enough pressure to make it stick well, while keeping the tape in the right position.
I also once widened a Pro-Filer gap with a file to handle an extra thick blade, and made the blade-end surface thinner to handle what Precision Blade Honing calls "carrier-held" blades (Matrix, though it looks like Paramount blades are like that too, as are many hockey blades), in which the available sides of the blade aren't long enough for the standard Pro-Filer tool, especially after they've been through a few sharpenings. I hated doing that. Such an expensive tool to potentially mess up, but it worked.
If you are super-super picky about centering, because your Pro-Filer is very slightly off center, you can use slightly different tapes on each side, or sand one piece of tape. But most recently, I mostly just turn the skate around every few strokes, instead. Especially if I'm not trying to create an ultrasharp foil edge, which requires that one be super-uniform and super-careful.
If you use a squish-able foam tape, the gap size doesn't need to be exact - elastic compression will do a good job of centering the blade, though you have to slow down your sharpening technique.
I think foam tape could also handle a side-honed blade (sides not exactly straight and parallel, e.g., dovetail cut, tapered, parabolic, etc.) - but I haven't tried it, because I've never had one. I'm not even sure that side honed blades are side-honed on the part of the blade the gap centers on - maybe only very close to the working surface, or whether that varies from brand to brand.
(I've thought of imposing side honing on an old pair of blades, just to see if it improves things - but I think that would be hard without a milling machine. Mike C. pointed out to me that even professional blade makers like HD Sports sometimes manage to add their side honing off center, which creates an interesting sharpening problem. Then again, he also pointed out to me that they don't always center the countersink on their screw holes right - maybe they don't use countersink drills? Ane everyone knows about their factory sharpening issues.), so maybe they just aren't as careful as they should be. Besides, I'm probably not good enough to tell the difference side honing makes. I'm not even sure what that difference is supposed to be - people have been debating the benefits of side honing skate blades in the same various ways at least as far back as the late 1800's. But I am drifting more off-topic.)