If you don't mind being a bit of a pr***, you could always use the GTS negotiations to bump up your JA. Once it connects you to a trade partner, they will then appear in your JA regardless if you make a trade or not. So you can just search and connect to people, quit and repeat. Bit pr***ish to people looking for genuine trades but it will get your JA up a bit.
Or at least breed some starters and version exclusives because some people on the GTSN are looking for basics like that --- FFXII Perfect game Inventory at 2400+ Hours - http://youtu.be/ALZMH7lvLdE