Looking at the privileges of CPL and MPL holders, I think both are the same with regards to acting as co-pilot. SASP 2 para 6 is saying that a pilot have 3 options to fulfill that time requirement. Either have 250 hours as PIC (P1). If there's not enough P1 time, you can "top-up" up to 180 hours of P1 U/S in a 2 crew airplane. If also cannot because the P1 time is really low to begin with, then 500 hours P1 U/S time will do.