For what it is worth, you might find you get the results you want if you just choose the blocking back set and put Gates in as your starting blocking back. I have Vernon Davis as my blocking back and he started off the season catching so many passes that he ended up sitting out a game with an injury despite having an A0 rating. He currently has 34 catches after 13 games.
Here are the instructions about the two TE formation:
Approx. Pass/Run Ratio: 55/45
Notes: Both TEs need to be quality receivers, 2nd WR not used often, both HB/FB carry the ball
Pros: Increased blocking for both run and pass plays
Cons: FB must be a large part of running game (at least 30+ carries per season)
I'm not sure that there are fullbacks in the 2016 set that you really want running the ball too much. There are only two (Ripkowski and Tolbert) who had 30+ rushing attempts and only two others (Kuhn and Olawale) who had more than eight. Seems like there are a lot more good players to choose from if you have a second wide receiver in your lineup.
That said, if you can't drop your scrub TE for a FB, then maybe you could drop Gates for another fullback and then quickly drop your scrub TE for Gates.