Coordinator + Repeater Xbee + End device configuration
You can have several devices communication with each other in all directions. What you need to do is to set all the XBee's to the same PAN ID, instead of configuring the destination physical addresses of the modules. The device you want to act as "repeater", should be a "router". If the end device, the router and the coordinator are sharing the same PAN ID, they will communicate to each other. So the end device will communicate through the router when needed, but if in range, it can also communitcate directly to the coordinator. The ZigBee protocol will manage that for you!