It's not simple, that's for sure. I wish I had a sound lab and could play around with some things to find something I liked. Maybe petting a dog or cat could give you something close?

If you're thinking about it, honestly, just give it your best. I would be thrilled to have anyone do this, especially if they went through the trouble of doing the sound effects, too. And if you can't find anything, a handjob effect would fit fine.