Lots of talking in the video to describe it, but I discovered a way to sync MIDI clock to the OP-1's tape transport so that you can sync drum machines, other sequencers, etc. to the OP-1's tape machine for multitracking madness. It's a pain-in-the-butt workaround, so hopefully Teenage Engineering will introduce transport sync in an OS update soon!
A note on the video format - I normally work in iMovie, but I had to use FinalCut for the different tracks of audio, and somehow I ended up with the video with that black border around it. If anyone knows how to get this thing properly sized (the project settings? resampling it? resizing it?), drop me a line!