Either crank it with the pedal to the floor (assuming no fly-by-wire throttle, which I think showed up in 98) or wedge open the throtle lever on the TB. Just don't forget to remove it when you put everything back together.

In the end, while absolute numbers are good to know, you are really more interested in how they compare between cylinders. Gauges vary in accruacy and I would rather see similar numbers, regardless of what the actual compression was. This means, do everything the same. But with all the plugs out, the starter spins the engine faster (less resistance) and with the throttle open, it makes sure each cylinder is full before it is compressed.

Michael