Subnet Routing for the Siemens PLC driver

It would be nice to add routing support in the siemens driver. The S7-300 and 400 CPU’s support routing of incoming connections to the internal fieldbus (MPI/Profibus). In complex installations, there is often a master CPU connected to the ethernet, the slave CPU’s are connected to the fieldbus.
As far as i can tell, it is necessary to add the subnet-id and the address/rack/slot of the target CPU to the connection request.
I know this might be a bit difficult, as Siemens did not publish details about the S7-protocol.