So, .. pay from the transaction fee and not any overhead on new users; avoid the pyramid sharing of those fees for several generations or tiers; and pay a short term burst of real reward, rather than a long term commitment.
We seem to be moving away from MLM, which is a good..
I would suggest in promoting this, that the tone should be noting the principal motivation is all about promoting BitShares and attracting those who understand its potential and become active users themselves, rather than this being considered just "the next big thing" for marketeers to leech dry.
Again I'll suggest, I wonder a short burst reward will drive this as hard as any MLM motivation. A short perhaps 1 year - 18 months time limit, will avoid unanticipated regret via compounding complexity etc; and will avoid new users resenting payments to a point they might just opt to start a new account and dodge that.
Lastly, I don't see why the reward for bringing new users could not be topped up from a delegate.. obviously, we want to avoid too much dilution and rewarding false accounts but where it is clear accounts were real and actively turning over transaction fees, the promoter who brought them in could claim their reward relative to that, after a time. Afterall, delegates get their profit from the transactions, so I don't see why a delegate couldn't be assigned to support this effort and perhaps other marketing, whatever else is seen to be making a positive contribution - though I can't think of any better atm than attracting active users. Just need to find the right balance that makes the effort worthwhile and yet see the benefits flow into BitShares rather than simply into the pockets of ambitious marketing types who adopt BitShares only for that $"opportunity".