Remember that the IPO can be managed by System Manager. So if you license these as a Branch, even though they function as a standalone IPO, then you can use System Manager to roll out the upgrades.
Talk to your Avaya SE, and hope they are not a generalist in Avaya but an IP office specialist in IP office. (yes, that is my pot shot at Avaya your new rollout of engineers that come from the Aura side of the business SUCK!)