pybombs prefixes and .gnuradio directory

[Paul Atreides]

I'm using 3 pybombs prefixes, but every time I switch between them i have
to delete /home/user/.gnuradio and let it autogenerate because all the
block paths are hardcoded to the last gnuradio version i used (i.e.
/home/user/prefix/gr39/...), if I don't delete the directory, when I open
GRC in, for example my 3.8 prefix, it tries to pull in all the flowgraphs
from the 3.9 session, some of which don't work.
What's the proper way to allow each prefix to have it's own recent history
and preferences?