Unfortunately, the ControlSpace architecture was only ever designed to work with /24 subnets which is usually not an issue becasue it tends to be used on an isolated network (or with other AV devices). There are two possible workarounds depending on the requirement to have it on the client network.
1) If the requirement is to access the ESP via ControlSpace Designer from a PC on the client network, then a possible workaround is to have a basic PC local to the ESP running Designer and then use remote desktop/VNC applications to remotely link to that PC from the client network.
2) Alternatively if the requirement is to be able to control the ESP using serial-over-ethernet then rather than connecting directing to the ESP via the LAN connection you could use a serial device server linked to the ESP's serial port and then connect the device server to the client network.
The remote desktop approach does work. I have personally installed a system like this with a customer who wanted to have remote access to the system. Even through VPN connection I was able to control the system.