Bukkit

Currently this plugin does a random teleport within an X and Z centred on 0,0.

I'd like it to centre somewhere else, if possible, so that I can guarantee players terrain generated in a recent patch instead of old areas.

So you want it to pick a random x and z axis and then random teleport them from that x and z axis to another X and Z axis?

No; instead of centring on 0,0, I want it to centre on (say) 6000,6000 and randomly place players within a kilometre of that location. That way I can guarantee 'new' chunk generation.