If slower people are properly on the right side of the trail i simply pass at a reasonable speed. A speed i'd pass my grandmother at! If someone is in the way on the left side, i say "on your left" which normally scares them into moving over. I got some new wheels quieter hubs (DT350s) and i'm now considering getting a bell so i can make some noise behind people. I used to just coast for a sec or two.
Paths can be happy communal places. Everyone is outside doing their thing. Don't F it up by being rude and in a rush. If you want to go fast take the road.