if you shoot at one of the big city ranges that has in house storage or its own blacksmith you could probably just swing a deal to leave them there to be babysit.
i know one range i use to belong to had lockers on site that you could leave pistols in for the odd fella who didnt want them at home.
but legally at the end of the day you dont need to worry about anything and you can just leave them where they are in your house as long as they are properly stored already.
i know guys that work over seas and they bugger off for 6 months at a time and just leave their shooters in the safe while gone.
im guessing there is probably a little more to the story then your sharing - living in a bad neighborhood or dont fully trust your roommates or some such thing.
what you could do is just meet a friend who has his restricted at the range and give them over to him for babysitting.
all you need for that is to just give him the cards for each pistol to take with him.
as you both already have your ATTs for the range to home no other SATT would need to be picked up, just meet him at the range and give him the pistols with the cards (which should be in the cases with your guns for transport anyways).
you could also just mail them to anyone who has a restricted card, say a parent or brother or such.
would just need the proper SATT to get it to the post office and they would need to get one to take it from the post office to their house once it arrives.
again all that you need to send would be the registration card with them.