No, I'm not sure if this is going to be "Tuesday's Theme" but that's what we worked on today, getting him to use those back legs to move himself around or position himself.
To do this, I did a lot of working on him to "back up", getting him to walk backwards. I did it both on all-fours and with him standing on just his back legs. What I did was hold my hand up (he thinks my hands always have treats, which is an advantage for stuff like this) and cue "back up" as I moved the hand back. At this point, he at least has the idea that he is to walk backwards, but in the beginning, he would whip around and follow moving forward. If he did that then, or happens to try it again now, I'd stop and start over, while giving my no-reward marker so he knows to try it again.
At this stage, it's mostly working on duration (more steps backwards before he resorts to raising up or whipping around, or sometimes sitting) and also on going straight back. Sometimes he ends up losing track of where he's going everywhere except with his head (which is focused intently on my hand - and the rest of him is angling in some diagonal direction).
It's almost the same process with him on just his back legs - except we're one step back in that I'm standing in front of him and "walking into" him to help him move backwards. Another difference is that he has to stay on his back paws. He can't drop to all-fours if he wants the reward. Otherwise, the process is the same and the things to work on are also the same.
He's getting a bit better at it and of course he likes the process and finds it fun (especially being on his back legs - he loves that and seems to naturally just do it - in fact, he first just did it on his own way back when). Perhaps this would be something of a "theme" for Tuesday, though I don't know if this is something I'll just want to work on once a week! It's certainly something we'll be working on for sure.