What's the problem with quality SF training being a little challenging? There is already a Jump Shot and Driving training regimes for forwards which is extremely effective.
I have no problem with needing to go through a little pain to train them in defense. If this means playing your SF as a guard or a power forward, that's fine by me.
"I don't know half of you half as well as I should like; and I like less than half of you half as well as you deserve."