How could I tighten up the steering on a 1999 Vauhall/Opel corsa with EPS?

I have 1999 Opel corsa with Electronic power Steering and finding when I am driving that the steering is quite light on the road, of course when I am parking its great to have the light steering but how can I make the steering tighter/heavier for when I am driving - anyone got any hints or tips on this please? - I dont suppose I can just temporarily switch off the EPS somehow to see how heavy it is and see how I get on with it and then reconnect the EPS if I want it back?