This is a bit hacky.
I know what you mean. Yes, have heard of Gimp but never used it though.
I also imagine that the Sweet Home bitmap could be inserted into an MS Excel chartsheet (I have an old 2007 version). If I have an appropriately sized/scaled box waiting in it the bitmap could be fitted into it exactly (the proportions of the bitmap can be maintained by holding down SHIFT while dragging its handle size) - of a little interest, to keep the centre of a picture in the same place and maintain its proportions CTRL+SHIFT while dragging the size handle works.
Drawn pictures in that version of Excel (also called vector drawings) are created from lines, curves, rectangles etc - those could be used to block the wall ends too.
I guess an easier way might just be to set up a series of 1 mm thick full wall width black boxes, within the appropriate walls, right in front of the Sweet Home 3D camera in the first place.
We'll see.
Thanks for your hint
