Rather than a simple coding to individually set the preferred units for (a) distance, and (b) weight, for some unknown reason the Garmin software implements a coding set that links distance and weight units into three specific restricted combinations of: 'Statute', 'Statue UK', and 'Metric', meaning you can't track in a combination of kilometres and pounds, or miles and kilograms (though you can walk in Miles and climb in Metres if you use Statue UK?)
I just added the S2 Scale and discovered that Garmin did fix this same issue on the S2 scale, so it is possible to display weight in pounds along with temperature in degrees Celsius (or presumably Kilos and °F): https://support.garmin.com/en-CA/?faq=HDRBWi3XbuAk4EswP7Mfe7
A search of these Forums (or just a Google search) shows people have been requesting this same functionality on their watches for at least five years, so it's not a novel request for Garmin to receive. Given they could implement this on the S2 Scale, would be great if they would extend this same consideration to their fitness watch line.