How can I inflate a presta tyre with just one hand
Get a better pump! Well, it seems the asker already has a good pump but I'll leave this here for others who might be having problems.

There are basically three types.


Pumps with a hose that screws onto the valve. Once it's screwed on, you can use both hands to operate the pump.
Pumps with a hose that grips onto the valve when you lift a lever. Again, once it's gripping the valve, both hands are free.
Pumps that you need to press down onto the valve to seal. The hand that's pressing the pump onto the valve also braces the pump against moving in the direction you're pumping with the other hand so, again, you're using both hands on the pump.


As you say, most pumps are designed to fit multiple valve types. In some cases, you'll need to either change a component in the head or use the correct side of the head so that the pump can lock onto a presta valve, which is narrower than Schraeder. (Actually, there are some presta-specific ones: my mini-pump that I take out on the road only does presta.)

You might find that a track pump is your best choice, since that allows you to pump the cylinder down with both hands, rather than pumping with one hand and steadying with the other. Of course, you can't bring a track pump with you on a ride.


Image from Wikipedia; there are plenty of other brands.