A senior aikidoka who used to teach occasionally at our dojo had a process for this. He'd demonstrate the technique, let people pair up, and then he'd circulate. If there were an even number of students, he'd practice with each member of the pair, doing the technique and receiving it. Then he'd move on to the next pair.
If there were an odd number of students, he'd practice with the odd man out. Then he'd break up a pair, send the extra guy to practice with the odd man out, and practice with the other half of the pair, circulating until he got to everybody.
I had a teacher who used to do this too - but only when the group was pretty small. But for some reason, the guy or gal who was the odd man out didn't join in someplace else but just waited for him to finish going through everyone and start showing the group next thing to work on. I think everybody felt working with him was compensation enough for having to wait and just watch a little while. He trained with you for roughly the same amount of time it took him to go through the rest of the students. And then of course in next technique someone else was the odd man out.
So this way he actually got himself more training than the rest of us, since he was training while showing the techniques to us and we were just sitting. OK, part of the "going through every student" may have been not training but actual instruction, so yeah, about the same amount of training as the rest of us.
The smaller the group, the easier for the teacher to train while teaching.