You can clutch an xb9s up in 1st and 2nd. You can get it up in 1st without the clutch, but 2nd you need the clutch(unless you want to stand up and bounce it, but I've never really tried). I've only tried 2 or 3 times in 2nd, and I took it pretty easy because I didn't actually have intentions of riding it up, I just wanted to see if it would come up. It came right up with a little slip of the clutch so there shouldn't be any problem getting it all the way up if you really try.
I would assume it's only coming up a little because you're hesitant to crash your bike, not to mention the xb is a lot heavier than the dirtbikes you're used to. Any chance your foot is pressing on the brake while you're trying to do it? That would keep the front end down. Have a friend ride behind you when it's not too bright to tell you if your brake light comes on as soon as you do it. I've seen plenty of people do wheelies and as soon as their front wheel comes off the ground their brake light comes on, just because that's an awkward angle for your foot.