This one comes up for me every so often. I tend to find there is little one can do on the merits of the code. Mainly it involves lots of talking. Getting inside peoples head, and convincing them one by one.

But I do think that sharing promotes sharing. A local code repository of shared code might help. Perhaps all the POD transformed to HTML and searchable from a web page -- your own mini cpan/search.cpan. Definitely more docs.

Also make sure you use others code -- set a good example.

But mainly I think it takes time, and talking