If it's a multi-lane road and he's on the right as a slow vehicle then cars should be passing on the other lanes. If it's congested enough that it's difficult to do so passing him probably wouldn't make a huge difference in the first place. I get what you're saying as there's places where I feel is safer on the sidewalk, legal or not, but everyone's judgement is a little different, and w/ the low visibility of a recumbent I could see getting on and off the sidewalk being especially dangerous.