Currently, I use
.nimble
You can do
import V:/src/anygui as vg
then use vg.someprocinvgYou can use cd V:/src/anygui && nimble develop (well, might have to change it to be DOS-compatible but hopefully you get the idea).
This will create a symlink inside Nimble for anygui and point it to V:/src/anygui. Then you can use requires "anygui" in your .nimble file. You will run into some other issues though, conflicting packages like this aren't well supported yet.