This is an excerpt from an old post by Bjørn Rørslett that was very useful to me. I would never have bought any pre AI before I read it
First, flip up the aperture follower (remember to set it back later !!)
Make an entry for a non-CPU lens if not already done, and mark it as non-AI.
Now, use the front dial to set the aperture to a value, say f/5.6. Rotate the aperture ring on lens to the same setting.
Then, either shoot in A or M, for the latter mode, you match deviations from "0" as normal by changing exposure speed.
Me again. If you use the f7 menu as I described, you can substitute "rear dial" for "front dial." Since you modified the front dial, you may prefer to keep using that.