The usual way I do it is to hit it, have it do the usual double bounce then hit it again... A think I started doing lately is practicing hitting it and only letting it bounce once on the opposite side.. You have to have both your hands up close together, and tap it quite softly and slowly at first, as it still comes back at you almost immediately, and you move your hands like you would twidle your thumbs.. It's awkward and needs a bit more timing at first as their is only one bounce between hits, but it's a fun alternative and eventually you can get it going very fast with your hands constantly rotating over each other in a small circle... Darn if I was at home i'd take a quick video of what I mean and post it..

I think you've got it though...

Personally I've found it kind of weird to practice slipping on the speed bag... I move shift balance between my feet and keep a fair bit of movement involved to get in an energetic rhythm, but like to practice slipping etc in other ways... That's just me though... I've seen others doing it successfully though..