they could join in group piano/keyboard sessions to learn basic fundamentals of keyboards i guess..some small institutions of music and art offer group classes for younger children up to adults here in my area..they go over really basic stuff..i suppose you could have them do these kinds of things to prep them for piano during that 2 year wait..
What I used to do was, I would keep people on my waiting list for one year. If I have a vacancy during the year from the time they first called me, I will call them and offer them the vacancy. If they have already found another teacher, I am not offended, and congratulate them, and call the next person on the list.After a year has lapsed, I will remove the student from the waiting list, expecting that they have found another teacher. If they are still interested, they may call me again.
look through all your students' practice records, and just boot the students who practice the least. Then you can create openings for new students. Plus, you get the added bonus that current students will work harder for fear of being replaced.
I think I will begin training my highest level students in the art of teaching, and what I expect from them...then I will pay them to train my "waiting list" students in the meantime, I am still in a semblance of controll, and can moniter thier progress vicariously through contact with my "student teacher" When a spot opens up, then the student will come to my studio...