The following download explains the steps required to configure two “out of the box” 215U-2 wireless I/O modules for back to back communications and automatic I/O configuration for 115S-12 & 13 Expansion I/O modules. 

It also has infomation on how to setup the 215U-2s for use with 115S-11 expansion modules instead of the standard 115S-12 & 115S-13.

This option does requires a configuration change to the mappings, the download has appropriate mapping configuration files and instruction on how to upload.to the modules.