I would propose an alternate solution. Since the number of such valid gateways is so very few, perhaps it would work well enough that someone must *be* a coordinator to set up a gateway whose outside-world address is in network 44.
Note it also involves routing subnets that belong to others...
I don't know how difficult it would be to add an extra property to a user record, should be a minute of work in a LAMP environment, I guess. Maybe a shortcut would be to add the "advanced user" property and initially set it equal to the value of the "coordinator" property. Then it can start operation quickly and should it turn out that really users require this without being a coordinator then later some kind of UI can be added to allow setting that. (by the users themselves, by coordinators, or by admins, whatever seems best)
Rob