How do I get my cat to give himself a bath?

A couple days ago, my cat decided to roll around in what I hope is some dirt. I really don’t know where he found the dirt to do it, but he did. And now, his normally white fur is a dark gray, and I have to go wash my hand after petting him. I would give him a bath, but I’m pretty sure it’s an even more horrible experience for him than it is for me. So is there a way I can trick him into giving himself the tongue bath he normally does?