Well, I ride a fixie about 99% of the time. But I also see the folks who simply won't learn to shift. They used be known as the "one speed-ten speen riders", back in the days of ten-speeds.
And yes, they're easy to spot, legs barely moving, helmet perched on the back of the head, chugging up even the slightest grades in a gear that is just way to high.
No easy solution here. I think any offers of help would only be met with anger.