Nighttime pottytraining?

My son will be 4 soon. He's been daytime trained for almost a year, and we started the nighttime training about a month ago. We did pull ups for a while but then moved to underwear. At this point, he does not get himself up in the middle of the night. We get him up to go before we go to bed and then at some point when we wake up in the middle of the night we take him (between 2:30 and 5:30am) For the last week he has been wetting the bed before we even get him up the second time. He sleeps very deeply so I think it could be a while before he wakes himself up to use the bathroom, he doesn't even wake up when he has wet himself. We do restrict his liquids in the evening, and he will hold his bladder for up to 5-6 hours during the day. Any suggestions, ideas? I hate to put him back in pull-ups but helping him change his pj's every night isn't going to work very much longer.