First of all what IOS version is running on your CUBEs as CUBE and SRST co-residency requires modern IOS versions.
Second, assuming your CUBEs can support officially SRST and you own SRST licenses, then if each CUBE is configured with its own IP address (not using box-to-box redundancy similar to HSRP) your only option would be configure 2 separate SRST references in CUCM and 2 device pools each pointing to respective SRST reference, and then split phones between the 2.