Not quite James, you can change the channels to feet, say distance, but the x axis at the bottom of the Time/Distance chart always stays in Metres, I have even gone to File. Preferences menu and changed Formats, Speed units to Mph. Always the axis on the graph is Metres. I think that this is the question..
You can change it but from what i've found you have to change the 'corrected distance' channel not the 'distance' channel.