maybe you could put
grenade = "smokeshellgreen" camcreate [getpos smokeshelllogic2, select 0, getpos smokeshelllogic2 select 1,1]
the last number is the height that it appears, i think in metres.
making sure that the logic is called 'smokeshellogic2' or whatever you want to call it.
Maybe you could put this in a trigger activation instead? over the waypoint?
either way it should produce smoke at the location once activated.
Good luck