Place a unit on the map (make sure it is on the same side as the player). In its init field put
emptygroup = group this; deletevehicle this. Give this unit the waypoints you want to appear.
What this has done is create an empty group with the waypoint path you require. When you want the waypoints to appear you can do so by joining the player into this group, using
[player] join emptygroup.
You'll get an unusual command ("1, follow 1") but it does allow you to make waypoints appear (and dissappear/reappear ...). Just be careful if the player is part of a larger group, or you are using other commands that rely on group names.
Cheers
[edit] bloody typos
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