Training a SF is not difficult. If he's got better outside skills than inside, playing him at PG will be no trouble. If he's got bad inside skills, use your third game to train him. The problem is people for some reason decide to train SFs with only outside players or only inside players. If you know you are going to be training inside for most of that season, train a big man.
Me personally, I'm training a 6'4 PG and a 6'8 SF prospect regardless of what I train that week. The other player I train is based entirely on what I'll be training that week....mind you they are usually 22-25 year old veterans.