Hello exilepanda,
The obvious answer is to copy your existing sitecustomize.pl file into the site/lib directory of your Strawberry distribution. But that will work only if the perl executable has been built with the appropriate compiler option, namely -DUSE_SITECUSTOMIZE (see the discussion of the -f flag in perlrun).
Looking at the Strawberry Perls installed on my computer, and also at the various Release Notes under http://strawberryperl.com/releases.html, the last Strawberry Perl executable I can find that was compiled with the -DUSE_SITECUSTOMIZE flag set is v5.12.3. I have no idea why the good folks at Strawberry began omitting that flag from version 5.14 onwards.
Sorry, :-(