What I was hoping for was each instance would be responsible for a video region (viewport(s) if you will) .. various gauges mainly. Was hoping I could 'poke' into the main pages VRAM easily.
As far as this goes, the easiest thing to do would be to use the main thread to change your resolution (you mentioned it's a full screen app), and then do something like this (with varying coords) for each blitz instance:
w=CreateWindow("", 0, 0, ClientWidth(Desktop())/3, ClientHeight(Desktop())/3, 0, 0) c=CreateCanvas(0, 0, ClientWidth(w), ClientHeight(w), w)
Then you could draw what was needed on each viewport.
As far as poking into VRAM, I'm not sure how you'd do that. You'd almost certainly need another library (like GDI or something) unless you wanted a Memory Access Violation.