There's no such thing as "using Gallo properly". The last 3 orgs he's been in have been the Twins, Dodgers and Yankees. It's not like these are stupid orgs/FOs that are throwing him at the wolves without a plan, Gallo just hasn't been good since he left the Rangers. Additionally, for a player as extreme as he is, he actually has pretty decent splits, career 111 wRC+ vs RHP and 103 against LHP, so you don't even have to hide him against lefties.
The only thing you're hoping if you sign him is that he cuts his K rate down to "reasonable", which for him is 35% at best, and then taking that with his positional versatility and running with it.