It will work as long as you're OK with it being locked in third gear. All you need to do is unscrew the coupler joining the indicator chain and the shift cable, and then unscrew the indicator out of the hub.
Does the indicator chain feed through a guide nut, or around a roller? If you have the roller, you should screw on an acorn nut. It needs to be a Special 13/32" Sturmey Archer nut.(Should be easy enough to get one from a local bike shop) If you have the guide nut, you can just clamp that in the trainer with no worries.