sharing a bed?

Our house has 3 bedrooms so the plan is to move Isaiah and Levi into one room and sleep on the bunk bed that's in Isaiah's current room.  It's a HUGE bunk bed with a full bed on the bottom and a full bed on the top.  The boys love to play on it and Isaiah loves to sleep in it.  We figured that Levi would be excited to sleep on it too, but we were wrong!  He has absolutely no desire to move out of his crib.  We've been mentioning it for months and he still refuses to entertain the idea of sleeping in Isaiah's room at all.  Since the beginning of this summer the boys decided that Transformers are really cool - not sure why - we had one Transformers book and they had never seen the movies/shows at the time (we've since rented the 1980s Transformers cartoon and they each got one Transformer toy for their birthday), but we were hoping that putting Transformers sheets on the bed would be enough to entice Levi into wanting to at least try sleeping on the bunk bed.  We gave them to the boys a couple weeks back...

and....no luck.  Levi still has absolutely no interest in sleeping in the bunk bed.  He wants his crib and that's that.  I'm not sure what we are going to do as baby's arrival is quickly approaching - but if he's anything like the older two, he'll be sleeping in our room for quite awhile anyway.  Levi has slept in my friend LeAnna's crib all along (because we had two cribs set up when he was born), so the plan is to get our crib out so at least the new baby isn't taking over his crib -- but we simply do not have the room for 2 cribs set up.  If anyone has any good suggestions as to how to interest Levi into the big boy bed let me know!!  I know in time it will work itself out, I just wonder when that time will be!