This is why I have a bell on every bike (except my go-fast), and a horn that I switch from bike to bike. The bell gets the attention of people using the oncoming lane to cruise (which is exactly what we're talking about here) about 90% of the time. Usually, we exchange "thank-yous"; the pedestrian/rollerblader/slowpoke is thankful that I'm giving some notice. The other 10% of the time, if they don't respond to the bell the first time, I blast the horn. This has always gotten even the most surly BMXer to move over. If I'm feeling especially reciprocally surly, and if time permits, I'll make a snide comment about the dashed yellow line. Unfortunately, about half the paths here don't have a dashed yellow line. No idea whether that's negligence, budget/staff time problem, policy, or what.