I haven't personally seen any examples of additional payment gatways being implemented into JobRoller yet, however this has definitely been done by ClassiPress customers. One example I can recall was a for a Dutch mobile gateway, but the customer hired an outside developer to create it, so did not share any information about how it was implemented.
The only suggestion at this point, if implementing more gateways now is of great importance, is to perhaps consult with one of the
AppThemes partners about the possibility of such a thing for JobRoller.