There isn't really a need to do this through a provisioning server. You can do this if you want but the phone's local settings will override the provisioning server anyway. You can access the settings via this menu sequence:
Menu > Settings > Basic > Preferences > Headset > Analog Headset
Make sure it's set to 3. Plantronics Mode; make sure you have the cable plugged into the 5 pin serial header properly and connected to your headset base and you should be in business.
I guess that is the problem, I do not have the Plantronics option only "Regular" or "Jabra". Can I rev the phone to give it Plantronics option? Is there something else I should be doing?
Confirmed all cable connections and they are correct. I can use the headset and it works just fine but drops the connection to the base after ~1 min. If I unplug the cables from the phone to the base, then initiate a connection from the headset to the base, it never drops the connection. To test I left it connected for 5 minutes. If I tried the same scenario with the cables connected between the phone and the base, the headset-to-base connection will drop in ~1 minute. This leads me to believe the IP550 sends the base some sort of signal and/or command (assume through the mini plug looks like a iPod headphones plug). Since I do not have the Plantronics option, I assume the signal the phone is giving the base is either not of the correct format or the wrong command or....
See attached pics for my current version(s)
Your phone has to be running at least BootRom 4.1.0 (which you have) and SIP 3.1.0RevB (Which you don't -- you are 3.0.1) to support Plantronics headsets with electronic hookswitch.
If you were to update your phone by setting up a local provisioning server, you could not ever point it back at your provider's provisioning server as it would simply downgrade to the software hosted on the provisioning server. To keep your phone working you would have to enter and maintain all settings manually or by using your local provisioning server. Honestly, this is a course of action I cannot really advise. It is complicated and requires quite a bit of knowledge to make work.
You should discuss with your provider or admin about updating the software revision and configration on the provisioning server. This is the most reasonable and sensible course of action. Honestly it should probably be done anyway for many reasons unrelated to the lack of support for Plantronics EHS.