XBee ZNet 2.5 (formerly Series 2)

I was wondering if Znet 2.5 modules can establish mesh network without a central coordinator.

Here is my situation, my devices are movable. When two of them come closer, I want to make them in the same network and communicate. If there is already a larger group around them, then they join the existing network. In this case, because I couldn't predict when my devices will meet each other, so I couldn't pre-assigned coordinator to one of them.

Is there any method I could establish this kind of dynamic emergence network? I was thinking either building the network without central coordinator or dynamic changing the configuration of coordinator to end devices may be a possible way. But I don't know how to implement it.

Any idea?