Even in single-pilot aircraft, some types of operations may potentially require a co-pilot or a cruise relief co-pilot, in which case one can log that time as P2 (per JAR-FCL 1.080(c)(2)-(3)). However, since JAR-OPS 2 (EU-OPS 2) does not exist yet, there seems to be no European regulation as to the scope of such operations in GA, and it's really up to the national CAA to decide.
Please correct me if I'm wrong.