What would a Rio/Garica 3B platoon look like?
I still see Comargo as the utility guy. He'd play most every game. Let him play some LF so he can be the defensive sub.
Any combination of internal 3B options would likely be below average.
Having said that, the Braves have an almost 0% chance of competing next year, and only marginally better chance to win 80+ games, so I don't think they should be worrying about fixing 3B this offseason. Just go with what they have and let the pitching continue to develop.