When someone mentions alternate currency, I think immediately about WoW badges of justice/frost/honor/butts/whatever. It can easily be done by copying that sort of system.
Make the points/badges/chotchkies untradable to players, limited in how you can acquire them in both gameplay and time constraints (so, for instance, you can only acquire X amount of points/badges/etc from, say, instances or PVP or whatever, and lock how many you can earn per day/week/etc), and make them only tradable to NPCs for certain rewards (which are also untradable).
This would easily tie in with the future instance content that was being chucked around earlier in the year by devs.