As a workaround:
Create your usual plan with metric dims. Make a new layer, where you'll put imperial dim elements and nothing else. Save a view with just this layer showing. Import both views and overlay them in PM. Use hotspots to align the views.
It's not inconvenient to work on because in your 'working' views, you can show both dim layers; maybe use different pens. Once the two drawings are placed, it's no extra work to maintain since they're both live.
Worth a shot? You're right that dimensions need a going-over though. Somewhere in here there's a wish for by-string control of dim settings.