First of all, I think you might no give 5 BTC to one person, who find the block (at least in 6th round), but increase payouts for everyone by 10% (that will be the same amount of BTC) or even by 5%. I think this is will give greater psychological effect for miners to join, than having a little chance to win jackpot (and this is why people often prefer large pools with stable little payouts than little ones with huge (as we may see right now) influence of luck).

And second suggestion is implement some kind referrals system for early stage or giving some bonuses for early adopters (such as, for example, 1% bonus for payouts to first 100 people who send at least 10000 shares). It can be temporary of course, all what we need is grow to 100-200GHashs.

I hope you understand what I mean (google translator is not always a panacea)