Rulebook states it must be on the rear.

If you are going for invisability, usually tyhe best bet, is to use a push/pull type of switch. Run the bar in through a very small hole.

Then remove the bar when you aren't at the track. Although, you have to have it labeled "push off" or something like that, so you may have to add a label when ravcing too. Very commonly done on street strip type cars.