Your game is exactly what we did in the puppy obedience class I went to. The trainer held the pup back while the owners hid, releasing the pup when the owners used their recall command.
My boyfriend and I still do this with our dogs. Now it is less for training and more for easy exercise
You've found something that works for you so keep it up. To address the pre recall running try playing your game in different locations, and at different times. We play hide and seek in our house. We take turns holding the dogs back while the other hides then calls the dogs.
I don't think you'll have to worry about your pup losing interest in the game... ours still haven't