If your other work colleagues are aware of his "nap time" ....wait till hes asleep tomorrow and either :
a/ change the clocks to 6pm all leave the office and turn the lights out, then get someone to go in and pretend to be the cleaner and empty bins etc he will wake up and panic hes been asleep all day.
b/ gather everyone round your desk quietly to watch him, then all yell at the same time and watch him sh1t his pants
c/ sneak round and re-arrange his desk items, or glue/cellotape some to the desk
d/ email your boss at the same time asking for him to come and see you urgently about something and point sleeping colleague out.
Although you know if this bloke gets found out and is awake all the time, you wont be able to post on AB so freely !