Odd, when even you're stumped, I don't really know what else could be done.
Can't you simply watch out for WM_PRINT/CLIENT and draw to the passed HDC, regardless of whether the window is hidden or not? As far as I read from all those topics and blogposts on google, it will only work when the target application supports it.
My windows in question are (hidden) pic windows, no ordinary @windows or dialogs.
Another way could be making your internal API available to DLLs, so they can also go the way /toolbar and others take - I think i read somewhere you draw to a memory HBITMAP and WM_PAINT it on the @window surface when required? I'd also be thinking along the lines of $window(@picwin).hbitmap, similar to .hwnd to stay inside the scripting language.
