I ended up using a twist lock, push pull cable mounted left of the driver's seat. The lock helps me make sure nothing moves on the track. I have a different set up in the back and used the factory arm on the lock out with a fabricated bracket. There are pics in my build thread.

If I remember correctly, Hobby Racer did a really excellent mod as well. His design would not fit on my transmission because we have different attachments in the back.

You definitely want this or finding 5th is a nightmare, at least on the track.