As a lazy option, if the difference isn't more than one or two inches, an additional knot or two into the sleeving of the longer line, on one or both ends.
Sorry, had to toss it out there... I don't like to spend a lot of time on my gear, and that's always worked for me.
If you've got more than a couple of inches excess though, you'll probably want to go ahead and move the sleeving.