What model phones, and not supported does not equal won't work
Do the upgrade to R11, change the Base Extension of all of the Digital ports to either blank, or some scheme that doesn't conflict with anything else. As long as you don't reboot, the digital phones will continue to function with the Users that were logged on before changing the base extension numbers. Create the SIP extensions with base extensions that match the users. At each workstation, connect the SIP phone, and when you register it tot he system with the User extension number and phone password, the digital phone go to No User, the SIP phone is up and running.