I'm not familiar with the X5DR so I don't know what types of filters you have available, but a wah effect is generally made by using a low pass filter with resonance.
You can set the resonance high, just under the level where it self oscillates (or where the filter becomes an audio oscillator by producing a sine wave) and assign a controller to modulate the frequency ammount, or to open and close the filter. Play around with with different resonance settings to determine the pitch of the wah, and different minimum and maximum frequency amounts to determine the amount of wah effect.
An expression pedal is a very good choice as a controller as it leaves both hands free but any manual controller will work (i.e. wheels, pressure, velosity, ribbons...) Depending on the type of effect you are looking for, you can also use an envelpoe or LFO as a modulation source. Don't be afraid to mix any of these controllers, you can get pretty wierd here. I hope this helps.