If I read this right, your advanced student is 10 months ahead of the beginners? Thats not a big difference. It should be well worth his time to work with other people, instead of keeping him separate. You also learn a lot trying to make your technique work on someone who has not yet learned "when to fall down now."
I have been studying my art for just over 20 years now. However, senior instructors can always find many things for me to work on, in our first kata / technique. (and its a very simple technique) So, when teaching people of different levels, they can all do the same thing, but focus on different parts. Some will be working on the gross motor movements, while others may be fine tuning different parts, others may be taking the technique in slightly different directions or from different setups. Or you might have different lengths of steps. Beginners are doing a wrist lock, intermediate are doing wrist lock into take down, advanced are doing wrist lock to take down to pin. With 4-5 students, work in a line, have one guy do his level on all the others, then switch the guy doing the technique. There are many ways for different level students to work on different things, with the same kata/technique. And its not bad for the beginners to see and or feel the advanced version, as long as they are ready for the fall.