: I have been meaning to find some shrink-tubing for mine -- Radio Shack,
: maybe?

You can whip the end of the cord using a thinner gauge line. It's quite easy and is in every Boy Scout handbook. Once whipped you could super glue it for a permanent fix. Using a contrasting thread to whip the end might look pretty nice, if you use good taste. Here is a link to an amazing site with more knots than you ever imagined existed.