Custom handles for custom properties

Hey there!  I'm trying out UMotion and it looks just about perfect for me, but I've run into some questions while trying to get it to work with a system of mine.

This system basically allows you to move/scale/rotate 2D textures on a 3D character's face, so you can do facial animation with 2D art.  I've gotten it to work fine with UMotion through custom properties, but the problem is that I can't find a way to manipulate those properties in a user friendly way.  Changing the numbers directly is too cumbersome, and the custom handle I made doesn't do anything while UMotion is locking the object.

So, the question:  Is there a way to change the value of a custom property through code, or otherwise set up a custom handle/gizmo for it?  I looked at the API and didn't see anything like that but I may have missed it.  I'm open to alternate solutions too.

Other than this sticking point it seems like UMotion is exactly what I was looking for!  Being able to work on face and body animations at the same time would be perfect.  

Edit:  After looking at the API again this might actually be a feature request:  Would it be possible to get a TrySetComponentProperty to go along with TrySetFkLocalPosition/etc.?  With that making the transform handle work with UMotion would be no problem at all.