The organization works best using peer pressure. I believe they will use the multilevel contribution award system. Provide lapel pin's,special Bibles,invitation to special events, lunch with the GB, a night in a lakeside suite at Warwick.
To the most loyal and giving members. then brother "loyal" can wear his gold JW.org lapel pin to the kingdom hall and to the assemblies to show everybody his loyalty by his special gift to the watchtower. I believe something like this would work best for this organization.
Here is a sample of giving levels