Thanks for the reponse guys. Ironically i actually found the answer to this question as soon as i posted. Doh!

I noticed in say for example a dyno pack dyno you can set an RPM limit where the car will not be allowed to exceed and hence you can go all the way to wide open throttle.

Totally understood the different load tuning concept i was just under how this was achievable in the real world but the Braking dyno answered that.

Thanks for your input.