It can't be implemented in Perl (well, unless you count the IE-only, plugin dependent, rarely installed, client-side PerlScript which might have the functionality).

To handle drag and drop you need the client to support it, and that means JavaScript. The JavaScript can then send the results of the action (e.g. Foo was dropped onto Bar) back to the server in whatever format you like and the data can be processed with Perl - but that's the trivial bit of the equation.