Ricoh 500ME aperture lock

For Ricoh 500ME, in order to lock the aperture in the 5.6 and the auto position.

I use my Ricoh for infrared photography, by experience 1/30 second and aperture 5.6 is a good starting point for the Rollei Infrared film (EI 6). However, the aperture ring slides easily so I wanted to lock it in auto -, and in the 5.6 position - hence this design. 

Auto mode:

5.6 mode: