Traces are not needed (and they are quite slow)

The simplest Method is
to create a "trail" in Med as a simple string
of vertecies.
(Or know the important vertecies in a more complex trail
model)

And then read out the position of the vertecies by code.

Once the player enters the trail (touching the trailobject), he is "locked" to
it. (the movement code goes into "slide on trail" mode)
The playerposition during the movement can be interpolated along
the vertecies of the trailobject.
You just need to be shure wich vertexnumbers to
use from the model.

Another method would be to export the trailobject to
a textfile, and use this textfile as basis
for the trailpositions.