When I go out as a single, I usually walk 95% of the time as it helps slow me down a little bit. Also most of the time when I am playing as a single it's because I'm working on something with my game so I never mind spending a little extra time either hitting an extra ball or practicing around the greens. I guess I've never expected to be let through groups simply because I was a single. The only time I expect to be let through is if the group in front of me is playing excessively slow (2-3 holes clear in front of them). And if they insist on not letting me through, I don't hesitate to call the pro shop.