Give an incentive to the Merit Sources for them to be proactive in achieving their quota.
They are merit sources and I think this is the biggest incentive. It's the honor, recognition and privilege.
What makes you think (your are sounding like you are not happy with them) that merit sources are not doing their job correctly?
Sorry but I do not mean that one. I am not saying that merit sources are not doing their job correctly. We just all know that there are times that they will become busy because they too have their own priorities (e.g. family, business, work, school, etc).
I think being a Merit Source is a tedious job hence I just think that giving them something in return is a wonderful thing.