SCT Controller experienced a loss of separation event when accepting non standard traffic from an adjacent sector that was in conflict with other sector traffic; the reporter listed non standard procedures as a causal factor.

Narrative

I was working the arrival/departure sector for CRQ/OKB/NFG/RNM airports. Traffic was busy with numerous arrivals/departures and overflights. A BE35 was on route from JLI to OCN on V458 airway. I received the hand off from the SDMR; Miramar Sector on the BE35 at 8;000 FT westbound along the airway as per the SOP for Southern California TRACON. Shortly after; Miramar RADAR called back and said 'sorry; I descended the BE35 down to 6;000 FT.' I had aircraft at 4;000 FT; 5;000 FT; 6;000 FT; and 7;000 FT ahead of the BE35's route. I said okay and planned on moving the aircraft out of the way. I turned a C525; at 6;000 FT; north-easterly to diverge away from the BE35; but made the turn too late. I estimate I had 2 miles lateral at same altitude before divergence had occurred. I wanted to climb the C525 to 7;000 FT; but also had southbound traffic north of him at 7;000 FT. The error would not have occurred had I not accepted a non-standard procedure and tried to make it work during a busy session. The BE35 could have stayed at 8;000 FT; been in conflict with no-one; and still complied with procedures.