Thanks for taking a look. It's a rather messy situation, isn't it :-)
If I can digest this stuff, I'll take it up again when I have more time and a stronger inclination. For the moment I'll just settle for the @INC that's being provided by 'INST_VER', and copy the contents of perl/site/5.10.0/lib into perl/site/5.10.1/lib. If you ever get any further with this, please let me know.
Thanks again.