Place of service code - administer flu vaccines

My Physicians agreed to work with a local Walmart to administer flu vaccines (just found out). Since this is not being done in our office and the majority of the patients will be medicare, I had contacted Medicare about what if anything would need to be done. I looked at the roster bill sign up for Medicare but it states to use for 3 or more places of service where a central billing office is used. Since it is just the one I doubt it will apply. A call and an email to Medicare has not...

Place of service code - administer flu vaccines