you can. You would use one channel for the field and the other for the armature.
You should keep one channel alway in the forward direction (the armature typicall) and alternate the direction on the other channel to make the motor spin in a differerent direction.
Note that is is essential that you never power the armature without current flowing through the field.
Also, note that this configuration is not optimal since the controller will have far more drive capability than needed for the field, and that the armature will only be using half of the bridge since it is never reversing.
We do have design under way for a separate excitation motor controller. Please contact us via <A href="dev.roboteq.com/dev1/contactus.html
if you are interested.