What we used to do when everybody was trying indexing on non-index equipment was to align the setup in the middle gear.
So for instance, on a 7 speed, you aligned everything in 4th.
That meant that any misalignment was only half in either direction and they usually worked.
Easiest to do if you threaded an adjuster into the rear derailleur, but if you were careful you could just set it up right on the rd cable clamp.