this is obviously a perl problem, you just have to write a little script that take whatever is in the clipboard/primary selection? and lowercases it, then you bind a key, say win+c to run this program. Then you can lowercase any selection any where with a ctrl+c win+c ctrl+v :) and in your specific case, shift+home ctrl+c win+c ctrl+v

Under windows it should be pretty easy, there was a post just recently about binding a key to a action, and Win32::ClipBoard handles the rest. I'm not quite sure how to go about it in linux but I'm sure there is a module for X somewhere.... hmm this could actually be quite useful... might have to look into it further :)