How about:
Pilot: "ATS, Callsign, Request ATZ Transit"
ATS: "Callsign, pass your message"
Pilot: "Callsign, Type, (From, To), Position, Altitude, ETA overhead"
The ATS operator would then be able to make an immediate impact assessment and provide traffic information accordingly. The 'Type of Service' agreement could be established subsequently if necessary assuming that there is a choice. In most cases in UK Class G airspace FIS would be the only option. The "ATS, Callsign, Request ATZ Transit" is the real attention-getter which the ATSU operator needs most of all in order to make the immediate 'impact assessment' prior to sevice provision and 'Service Level Agreement'.
A typical response could be:
ATS: "Callsign, report overhead, traffic is........, Flight Information Service"
.....nice and simple.