How can I inflate Presta valve tires using a Presta compatible pump without bending the valve stem?
I've never had this problem.  It would take considerable force to bend the stem.

First be sure you have the nut on the Presta stem, and that it is screwed down firmly against the rim (though it shouldn't be wrenched tight).  This will keep the stem from wobbling around in the rim hole, and makes the whole job easier.

Then make sure that the wheel is rotated around to where the stem is easy to reach, and the pump is pre-positioned so you won't have to fight the hose to get the chuck on.

With most chucks you press the chuck on, the raise the lever on the chuck, but a few you raise the lever first, install the chuck, then flip the lever down.  Be sure which style you have.

Prepare the chuck for installation, press it on squarely, then, while holding the chuck with one hand raise/lower the lever with the other.

Note that on some chucks there is an adjustable collar on the end of the chuck which you can screw in for a tighter fit, out for a less tight fit.  You want the collar (if present) adjusted to allow the chuck to slide on with only mild resistance, then grip firmly when the lever is raised/lowered.