I'm also curious about this.
We don't have to always lose infinity focus, do we?
The Pentax flange-to-film (or flange-to-silicon) distance is 45.46mm.
The Nikon distance is 46.50.
So the distances are right -- the Nikon distance is greater than the Pentax distance.
An adapter that will focus to infinity is theoretically possible, unless there is an issue with throat diameter. If the Nikon lens won't fit into the diameter of the Pentax hole, then that creates a problem.

But I don't see the problem. I just happen to have the required parts for the test in my hands because I'm one of those guys who loves to collect legacy lenses and use them on a new digital camera with adapters.

A Nikon N/AI lense just went into the socket on a Pentax-K 2X doubler, so throat diameter cannot be the problem. Now the prongs on the bayonet mount are not exactly correct, so it won't twist and lock. I also see a small black "bump" or prong sticking out of the back of the Nikon lens that is getting in the way. Maybe grind that off?

Is hacking the Nikon lens to permanently adapt it out of the question?
(That is a personal decision, and depends on whether you wish to ever use the Nikon lens on a Nikon camera again.)