Here's something on using borax: http://www.extension.umn.edu/yardandgar ... borax.html
. It sounds like if you don't intensively plant something to replace the Creeping Charlie, it will come back. Is it in a lawn now, or what do you want to have growing there instead?
Either way, it sounds like something worth a try. And if it starts coming back in lesser amounts, it would be easy to keep at it by digging it out.