Yes, non-AI lenses can be shot on Pentax DSLRs. Some of these old Nikkors actually turn and lock into the K-mount, believe it or not. But more of them turn only enough to safely hold their own weight. I have tried the setup, with great results. Of course, you must use manual stop down metering, but so what. You still are offered the opportunity of shooting old Nikon glass on your Pentax-- a great experience if you ask me.
If you express further interest, I'll dig into my resources and provide and old DPreview thread, by a guy named Carpenter, who did some pioneering work here. In that thread, he actually gives some specific lenses which will lock onto K-mount, as well as others he tried which only turn enough to hold safely. Also, if you wish, I'll even post a shot. Their are others at this forum shooting old Nikkors on their Pentaxes too. I have seen plenty of threads with examples of various lens combinations highlighted.
Of course, as always when discussing such efforts, there are no guarantees--so proceed with caution. Just because I have not had a problem, nor read of any problems ensuing form such adventure, it does not mean a problem can not develop. After all, there is nothing in the owners' manual about this.