Remind me how old he is again?
You can swaddle with just his legs in the swaddle -- I did find it was harder to keep together that way and we ended up with loose blankets. A sleeping bag works just as well as a sleep cue and I think it feels similar to the swaddle on their legs (or you could also wrap a small blanket around his legs inside the sleeping bag, that way the blanket won't end up loose in the crib).