Update: I've added a tiny 5 line function to allow any external addon to specify which minimap frame GatherMate should draw its icons on.
As such, I have also added 2 lines of code in Chinchilla Expander to re-parent the GatherMate minimap icons on toggling it, with ckknight's permission. So just update both.
Thank you thank you thank you! I was just about to sit down and attempt it on my own. Works great by the way!