You can make a clamp-on headrest that's removable as mentioned.
Say, 4" or 6" square, padded, supported by a length of tubing with a clamp.
Weld the forward side to the headrest support, and use a 2nd piece at the backside of the crossbar.
Bolt the two together for track use.

My car had one in it before I got it, and it's been handy ever since I got the thing into the 10s.