The OP has probably moved on, but for anyone else looking here, my approach was to tackle this from the windows clipboard side.
For background: I keep a list of my credit card info in Keepass. Sometimes (poorly coded) shopping cart checkout forms don't like spaces in between card numbers. I like storing them with spaces since it's easier to read off that way.
There's various Windows clipboard utilites out there, but it took me a while to find one that could do some processing on the clipboard contents and pasting it out - Clipboard Help and Spell
The program has a way to "save" a bunch of text transformations, and even assign the action to a hotkey.
For reference, my "Find and Replace" action is to find "\s" (without quotes) and leave the Replace textbox empty. "\s" will match whitespace character.