my brothers 30th was on the 4th November last year, and we threw him a surprise bonfire party at home. we had fireworks, a bonfire cake, sparklers, a 'guy' - he loved it!
awkward one with the invites...has he got siblings that could perhaps help with rallying the troops together? not bypassing his mum or anything, though saying that you've got months yet! the closer you can leave it to the big day the less chance there is of someone accidently letting slip. if you watch gavin & stacey, it's exactly like that leading up to a surprise party!!