Hi,
if there is no "darkness" on any of the range of the dmx channels (fixture is alwas on/lighting), then probably not, because what the fixture's mechanics and firmware does not allow, the desk cannot force from.
But I cannot believe, that these fixtures does not have a dimmer function. Is not a dimmer a part of dmx range of shutter channel, like: 0-50% dimmer, 50-100% shutter/strobe? In old times that was quite usual. Try to use Beam Raw fader of shutter of dot2 and go from 0 to 100%.
If so, you can open the fixture personality in the editor and change Strobe (under Beam) to Dimmer, then change this new personality in the patch.
Then dimming will work with wheel and highlight and the only change is, that strobing is then controled under Dimmer attribute.
Edit: If the fixture is always on/lighting, the only mechanical way is to insert a solid circle instead of a gobo or color glass and use this as a dimmer 
A@