Yep - this would be ideal... and what i tried first.
The problem I was facing was that I was creating a full COMPOSITION layer in VDMX5, using Blendy and then finalising in Madmapper, but this meant that Madmapper was really only allowing Quad Pin corner adjustment, as it was "one whole layer" coming back in, so for perfectly flat edge blending this was ideal.
My final 3xScreen TripleHead2Go projections were on to slightly irregular surfaces so I needed to be able to actually adjust the original layers, corner by corner.
This is where I find VDMX a little bit limiting and not very precise.
Madmapper allows for much better adjustments, and so having this as the "stage" where I can do final tweaks and adjustments would be ideal.
I appreciate this is a slightly longwinded way of doing things.....
I have tried Millumin as well as this interim stage, but the "skewing" seems to add jarred pixels too much, and loses the original smoothness.
I am in the process of creating an iPad function for TouchOSC that allows me a bit more precise control of VDMX5's sizing options, but am certainly open to any other options