Bard and David
Obviously not Pentax, i use a Canon Right Angle Finder, and wouldn't be with out it, it is brilliant, and i can get sharp focus by eye only 90% of the time.
Never used software ever, i don't think it it's necessary,
I'll probably be shot down in flames for this, but what the heck, it works for me.
I cant see why a good Pentax one wouldn't work for you, but as stated before it must be on a Matt Focus Screen
Leon