The USPS plans to sell off the downtown Berkeley facility and have a smaller scale storefront Post Office nearby. I suggest instead that the scope of USPS occupied space in the existing facility be reduced and other Federal agencies move in.
The first other Federal tenant which comes to mind is the Berkeley Social Security Administration office, presently across the street (2045 Allston Way) and maybe 100 feet closer to Shattuck Ave than the Post Office on the ground floor of a parking garage.
If that is not enough there is a Marine Corps office with regional responsibilities for recruiting Marine Corps Officers located at 64 Shattuck Ave, also quite nearby.
The lobby of the current downtown Berkeley Post Office could easily serve as a waiting room for Social Security claimants. The SSA office in SF Chinatown is/was in an old branch bank with similar counters, etc and it looks great.