How to set up punch out supplier security by business unit in eProcurement?

Hi

We have two punch out suppliers that set up via direct connect in ePro. We are required to set up security so that requester can only use specific punch out suppliers based on his/her business unit. How do we set up punch out supplier security by business unit? It seems like we could set up all punch out or no punch out but not by supplier.

Thanks for your help

H.