I do not have an X1, so my answer is based on other synths. In the first place, pitch bend is a continuous controller. I would guess that the sustain pedal is a two-way switch. So if you use the sustain pedal to control pitch, you will not get a continuous effect. A volume pedal would be a better bet, I think.
There are devices that can map any controller to any other. There is a company called Midi Solutions that makes devices that do this, and they are inexpensive. However, another problem you face is that pitch bend is a "centered" controller. In other words, you want it to default to a central position. A volume pedal would not do this. If you only want to bend in one direction, a volume pedal might do.
I have not given you a solution, but some things to consider.