If you look at the training system a SF trainee has to play anything but SF to progress in single training, PF too .
You can train your SF and still play him as an SF. It's called multiple position training.
You want to train your SG ? he should play SG, you want your C to have some SG skill ? he should play SG.
Easy: Multiple position training.
Multiple position training.
"Air is beautiful, yet you cannot see it. It's soft, yet you cannot touch it. Air is a little like my brain." - Jean-Claude Van Damme