The most effective program to encourage playing is to attract new players who will actually play, rather than wait for the next freeroll.  Sources of new players who will play include

• players from other internet poker sites who may appreciate low rake, anonymous poker
• people who already have Bitcoins but do not currently play internet poker
• live poker players

Getting someone from one of those groups to download the software, and try it with some chips, is the key ingredient.

Freerolls are part of the big picture.  The Affiliate program has a greater potential to give long-lasting incentives to SwCPoker players who find more players to play.