Posterize-time/stutter frame post-processing shader for camera?

I have no shader writing experience but I'm looking for a way to hold frames so the framerate appears to be rendering at a lower rate. For instance, if the game runs at 60fps, and I want the camera to appear to render at 30fps, every other frame would be held still. I'm trying to emulate 35fps, but the option to set any variable would be best. I assume this would be a script placed on the camera and linked to a seperate shader that would do the temporary frame buffering and freezing.

I've tried using application.TargetFramerate and renderTextures with cameras to produce a lower frame-rate effect, but all have their side-effects with mouse raycasts and rendering software cursors, and I can't use hardware cursors as they are too small.