have a trigger where he is supposed to drive but gets hurt, that covers as much of the road he will use as you can. Group it to him, and use Vehicle Present to activate
on activation:
UnitName addeventhandler ["hit", {this exec "SetDammage.sqs"}];UnitName addeventhandler ["dammaged", {UnitName setdammage 0}]
(of course you could also have a looping script to provide his current health and set it to that for the dammaged script, which would probably make this work, if it doesn't already)
and on deactivation:
UnitName removeeventhandler ["hit",0]; Unitname removeeventhandler ["dammaged",0 or 1 (not sure..)]
or:
UnitName RemoveAllEventHandlers but that will only work if he doesn't have any others yet
Setdammage.sqs _dammage = getdammage unitname
~1
unitname setdammage _dammage
exit