I was wondering if there is a more general way to figure out where the $Config{libperl} lives

I think the following would always produce the correct path on Win32 to $Config{libperl}:

perl -MConfig -e "print $Config::Config{archlib}.'\\CORE\\'.$Config::Config{libperl}"

Works for me - and on Linux if rewritten (with corrections to the directory path separator) as:

perl -MConfig -e 'print $Config::Config{archlib}."/CORE/".$Config::Config{libperl}'

Attend to the path separator issue (if that's applicable to your needs) and you should be able to come up with a truly portable script.

Cheers,
Rob