could get expensive if you are having to buy a domain per offer.

Crazy idea for tonight

Could you setup another site some thing like freegiftsgiveaway.com/members/july/ then a image with offer

password protect it

make it look like a membership only website and then post the password to a few sites.
Then change the password every few weeks and people will be going crazy when they can not get in then a few days later post the new password.

People go crazy when people get some thing for free and others miss out.