If you use the CPAN module to install modules:

perl -MCPAN -e shell
[download]

then you can configure some default arguments, so you can have the PREFIX put on automatically. The first time you run the CPAN module it will prompt you for options like this, and PREFIX is one of the examples given in the prompts.

It's what I do, to install modules in a non-system location for easy housekeeping.