A little preparation is in order. Have a fairly high resolution photo of yourself, taken looking directly into the camera, and crop it pretty close to your face. Here is our result with a little tweaking:
Lloyd and Peggy Morris as Simpson Characters
So sit back with a large box of multi-colored donuts and have fun. If you make a mistake while customizing your character, just give it a big "Dohhh!" and hit undo. Notice I added what has been my daily uniform for the last couple years (black t-shirt) and Peggy's funky, retro glasses.
I recommend that, if you what to get the true Homer Simpson experience from this, you should do this at work on your office computer. Then, take a good long nap after you finish.