Yes, you can "cultivate" calluses. If you were to methodically take a rasp (or a brick, or any rough surface) and give your left-hand fingertips a modest scraping with the rough surface, you could build calluses there. Now I don't mean that you should scrape the fingertip off or anything: but your body WILL respond to the additional stress on that area by gradually thickening the skin there.
You have your doubts? Try doing this somewhere on your body that normally doesn't get calluses: your forearm, your palm, the front of your thigh. Trust me, your body will respond to the "wear" on your skin by toughening the tissues there.
Personally, though, I find playing to be a more gratifying way to build calluses.....
