Well, then, can you mechanically create those stresses? Regularly send electrical signals to exercise the muscles, increase and reduce pressure and temperature (even have robot-controlled plates do a full massage), stretch and vibrate the whole setup, cycle through levels of certain hormones...? It may take some experimentation, but once you figure out a process that works, you can grow millions of organs with it.

(The story "Mazer in Prison" mentioned, offhand, someone getting his muscles electrically stimulated while he slept as a substitute for exercise.)