I'm going from memory here and away from my BIAB workstation, but I think the trick is to set the notation to triplet resolution, then enter each triplet as follows: start on the first triplet "bar" and enter the notes on every other triplet: i.e. triplet 1 of first group, triplet 3 of first group, triplet 2 of second group, etc. This should display and play as quarter note triplets.