M.M.
If he's truly sleepwalking, he won't know he's doing it amd bribery won't work like it does with potty training (take it from someone w/ a history of sleepwalking) --- Talk to his pediatrician; perhaps he could help you find the underlying cause. (In my case, high school graduation, college finals, movingand the like)
Good luck
M. M/
45 year -old mom to a beautiful eegetic 7 year old boy and married to a great guy(BTW I haven't slept walked in about 20 yeaes)