I wouldn't put the two together. The turtle could end up eating the hermit crab or the crab could latch on to the turtles foot. The set up would only stress the both of them out, and stress can lead to death.
Can Turtles And Hermit Crabs Live Together And If So How Do I Care For Them?
Please do not attempt to put them together! If you need info on hermit crab care, visit hermit-crabs.com. Many websites and pet stores give bad info for their care, but this one you can trust.