Look no further than a cackle-worthy mod recently developed by a Reddit user named ranier511. It's basically a layered Photoshop file, ready and waiting for your avatar's closeup. All you have to do is rename it LoadingScreen.jpg and use it to overwrite the image in your Program files/Electronic Arts/Bioware/Star Wars – The Old Republic/swtor/retailclient/LoadingScreensfolder. PC Gamer has a few examples to get your creative juices flowing, and you'll find the original thread on Reddit.
[Update: Goldnames on the official forums have warned that mods like these can corrupt your game installation, so install them at your own risk!]