@INC has a hook mechanism, where you can place a callback instead of a string path.

The callback can decide to return the code if encountered by require while working thru @INC.

The interface is a bit convoluted but it works. After adding the hook inside BEGIN you can call use or require deeply hidden inside foreign code and your "RAM modules" are installed.

quotes from the docs

You can also insert hooks into the file inclusion system by putting Perl code directly into @INC. Those hooks may be subroutine references, array references or blessed objects. See "require" in perlfunc for details.

...

You can also insert hooks into the import facility by putting Perl code directly into the @INC array. There are three forms of hooks: subroutine references, array references, and blessed objects. ...

edit

here some example code from an older discussion

• --> [WEBPERL] dynamically importing non-bundled modules via http

in that case the code is fetched via HTTP, but it should be easy to to just fill in your RAM stuff instead.