the campaign admin should be able to set a list of statements that donors will broadcast

[pdaire]

I believe that a Retweet is not the same as "your friend" talking about something. I suggest that the admin populate a list of statement (it could include pictures) that randomly will be broadcasted through the donors, eventually the admin could set different lists of statements and the donor could pick which is more suitable for him/her i.e. in a campaign against to a hydroelectric power station you could set a list of "forrest friendly" statements another list of "energy efficient", etc

BTW: great software!