I don't know about C-More specifically, but in general this is a capability of many MMI's. First you'll need one that allows for multiple PLC's in the tag database format, and also one which either has two ports with which to talk to the PLC's or an RS485 capable port, or many of the newer MMI's have ethernet. The PLC's hopefully have ethernet or 485 as well (AD's do) or you should be able put a little 485<->232 converter in front of each PLC.