Counting steps when using a rolling walker (rollator)

Recently, my girlfriend and I were on a city trip that required a lot of walking. When comparing our steps and distance in the Health app at the end of the day, my steps and distance were not half that of hers. As I'm using a rolling walker, I suspected the lack of wrist movement was to blame.

The next day, I left the watch at home and carried the iPhone in my pocket. This resulted in much more comparable results - I know I take longer steps than she does, so didn't expect it to match completely.

So here is the question: how do I tell my watch that I'm "physically challenged", and the step counting should be left to my iPhone? And Apple: shouldn't the watch record this discrepancy automagically?