I've actually been trying to compile GIMP for Maemo directly (none of this in-EasyDebian crap. Chroots are nice, but I don't want to go through one just to run GIMP); it loads a tad slow but runs fine, more or less - however it also definitely isn't usable currently because doing anything aside from using the brush on the drawing area (including using key shortcuts to select other brushes/tools) breaks input into the image area - it also breaks input into some other apps, like inside the web browser (MicroB - address bar input works fine, the stuff inside the browser itself though, doesn't register clicks). Way out of my skill to fix, though if I fixed that I would eventually try to hildonize the UI.

In the meantime, I don't really think there is an app that does exactly what you want.