I have to agree with Pat about carrying him out - wake him up and carry him out. There have been times that my 7mo boy hasn't gone before bed so I let him go to bed, but then about an hour after he goes to sleep I wake him up, take him back out and sure enough he goes.
If he really hasn't gone outside since you got him, so you haven't been able to praise/treat him for going outside - maybe set aside a good chunk of time one of the days this weekend. Feed him, heavy dose of play, walk him and just stay outside with him until he finally goes - even if it is a couple/few hours. That way you get to see him go, and have the opportunity to praise him and give him a treat as soon as he goes. I was always taught to chant softly something like "potty, potty, good potty)".
Do you praise/treat your other b when she goes outside - because he should pick up on that as well.
Also, do you know when he goes in his crate - does he go right after you put him in there or is it more when he wakes up from a nap?