I agree that there probably needs to be greater risks associated with tanking, as it does sound as if there is probably too much incentive for a team to shoot for finishing 6th over 5th and not enough repercussions. Although this is only my first full season, and, personally, I'd love to finish 5th so I don't have to worry about being relegated back down to Div V.
Another option, in addition to the ones you brought up, might be to have the two 5th place teams in a league play each other a home-away series during the playoffs. That way each 5th place team does get two games during the playoffs for training and some arena revenue. Although perhaps that would result in people tanking from 4th to 5th, as 4th place likely doesn't get too much from the playoffs unless they can pull off a bunch of upsets.