There is no way to help a association member in the game, other than collecting building bonuses. So if a member has financial problems there is no way to help him. So what if member could invest in train station buildings like the laboratory or the engine house.
Lets say a member invests 500k in a members lvl 9 laboratory dropping the price for an upgrade from 2m to 1,5m. And since the member invested 25% of the upgrade price he would also get 25% of the prestige when the building gets upgraded. There could also be limitations like every member can only invest the equivalent of upgrade price divided by amount of members in the associated.
Example: a association with 10 members can only invest 10% of upgrade price each.
It could also just be a flat percentage restriction.