I gather what you call 'lease' is what I would call 'loan'. I can sort of understand why you'd want to do this, but most people I know loan horses as they have other commitments in their life, such as going to university, which prevent them from having time for their horse, but after a period they will be able to regain ownership of the horse once more. Loaning a horse is usually over a long-term period, and once you've had another person riding him for a few years, you might find he has changed. I knew someone who loaned her horse for a year due to pregnancy. When she got the horse back, he bucked and spooked at pretty much everything in sight, and the person she loaned him to was a so-called 'professional trainer'. I would be wary of creating a new figure who has completely different riding techniques and horsey nature to take your role. Also, once you've agreed a loan, you could start to miss him, and it would be difficult to get him back!

As Eva said, sharing is a good idea. That way, you can still monitor how PJ is getting on, and correct anything you think is going slightly wrong.