You've already got a pretty good solution in place. If you're rules don't allow for a new owner to take over mid-season or if you're rules don't cover this situation, and your owners are ready to mutiny because they don't agree with the solution, however, another alternative is this:
You post that ghost team's roster here in this forum each week, set up a poll for each position, and let the Cafe vote on who to start on that team. We are all fairly opinionated and also have the advantage of being impartial, since we really don't have any skin in the game regarding who wins your league. If that team makes the playoffs being managed by proxy via the Cafe, so be it. If that team wins first overall, you can then either role the 1st place prize money over to next year (incent return owners) or alternatively, just allocate the 1st place prize $ out to 2nd, 3rd and 4th or however many spots you were going to pay anyway, based upon the payout schedules for those spots.