Adsense don't works ... The traffic is about 350-400 uniques per month mainly from US and mainly from Google.
Have you tried CPA ads? How about Commission Junction or Clickbank for game related products? Think about who your viewers are and what are they into. Look at what is related to gaming. How about free ipod/ipad email submits? Another option is to look at other gaming sites and see if they have an affiliate program. I'm sure you could find plenty of those.
Oh but it might not make sense for him if he's got 300 odd hits a day. CPA might not convert that well in such hits.