promote a hashtag? either literally by sponsoring a promoted trend, or just by adding a hashtag to the tweets your apps generates.

at the moment, you ask users to tweet eg "@betnext 5000 on SomeTeam - Feb 7th 2011"

Change that to "5000 on SomeTeam Feb 7th 2011 #betnext". to me a hashtag is better promotion than an @reply.