It sounds like the only way to "beat" this is to try to find some unrelated feed of noise to base the key presses on. Because when you actually do think about it deliberately, you fall into a pattern.

One way to do this without an external data source might be to just visualize (or look at) each object in turn clockwise of a room you are familiar with. Or use any other random source of data. Then come up with a rule that applies about half the time to some objects and half to the other. Or rather, come up with the rule before thinking of the room.

Maybe count the number of letters in the name of the object. If it's even, hit the f key, and if odd, hit d.