Dont know if it helps much, but you can use pXent_setcollisionflag and EVENT_FRICTION to set up an event function for collision of physics entities to other objects. Than you could manually write something where the if the car collides with something else, the drivers is throwed forwards through e.g. pXent_addforcecentral.

But my quess is also that the physics part of GS3d is outdated, so difficult to use for more complex situations like of this thread.