Although I'm having a hard time imagining what you might need this for, and I think it'd be better if you explained that and showed us a SSCCE: use is like BEGIN { require Module; Module->import( LIST ); }, and require is like a do which first checks if the file has already been loaded (via %INC), and do is like a fancy eval. So the answer to your question is likely* eval, although of course that comes with serious security considerations if the code being executed is not 100% under your control.

* Update: The @INC hook mentioned by the others is certainly a possible solution as well.