On our past trips (in May) we didn't use many FPs because crowd levels were low. But we would get a baby swap pass b/c DS was so little.
The second scenerio that you offered up never occured to me. It sounds like it would work. Here's what I would do--Go up to the CM at the standby line. When you go up to get the baby swap pass, don't even show them at that point that you have a FP. Then after you get the baby swap pass, you pocket the baby swap pass while your DH and DD take 2 FPs to go ride. I don't see why this wouldn't work.
I might have to keep this strategy in mind for the few rides that my DS will be too little to ride. I love getting good ideas from the DIS--a great reason to read other people's PTRs/TRs!!