Thanks Guys,
it took almost 5 years, but this was something I had in my head from the early days of GuiTools. However, often it takes time to see how a project will evolve and how all parts play together, to find a way and get a clue how "relative" easy you can implement the next thing. In fact the hardest part here was to go thru the entire source base, changing all image references to use either _SOURCE or _DEST, instead of a fixed handle to the main screen. If I recall correct, it were some 400 references to change, and you may guess how often I had to go in again, cause I found another reference, which I've missed before :)