I know I'm awakening a dead thread, but just a thought...
Suppose the lava flow cooled, and hardened. Now, take into account that cooled-off lava rocks, are very sharp and rough and incredibly difficult to drive over. This would mean that they would be almost impassable.
Now, suppose it was only the surface that cooled. You could have a special "lava-rock-tunneler-thing (insert better name here)" that would tunnel through, making a hallway of lava walls that you can drive through quite easily, with the still-hot, flowing magma on the other side of the wall, hidden underneath the hardened layer. You can also set a small "booby-trap" on certain sections of wall with a StarFlare GP, which would be set into the wall and hidden (invisible). This would go off if an enemy approached, killing them and setting the lava flow loose again, sealing off the passage. Also you could build a Magma Well on certain places if say, the surface cooled and a meteor hit it, creating a Magma Vent.
Like so:
End result - very good shortcut through the lava flow.