I interact regularly with GTK+ developers, and have been a regular contributor to GTK+ on OS X. They don't want our patches - they are very specialized and intended to deal with cases in Ardour that are not really a part of ordinary desktop apps. GTK+2 is now in maintainance mode anyway.
If you've contacted GTK about upstreaming your patches, what was their response? I'd be surprised if they didn't want to.