I haven't tested this, but can't you do this in your .pm module?

{
  local %INC = .....;
  # Work, profit!
}

# %INC reverts.

# Work on things that require an unadulterated %INC...

1;
# Leave work by 5:30pm.
[download]

It seems like this is mostly what you are accomplishing by storing %INC's value in a lexical, and then restoring it later, except for the issue of lexical vs dynamic scoping, which is why I mention I haven't tested. ;)