I'd recommend remc's Fat Dude, even though it isn't a Michael character, since the character has some clothing. The only problem is that his website, Third Eye Function, is having server problems.

You can do a search here in Free Stuff for Fat Dude and download version 2.0 of the character, but I don't think you can download the full Pack which includes the clothes.

momodot has a product here in the Marketplace called Morf Man, which is basically the P4 Male with a lot of morphs (including fat morphs). And Michael already has built-in fat morphs (Mike 2, anyway).

The problem with using morphs on existing characters is that you'll have trouble getting the standard clothes to fit (although a morphing clothes update for Michael is coming soon).