Let me first say, I don’t know the answer, but I think I can offer a different perspective.
Let’s analyze the berlinclock clue, and translate it to usable Sanbornese. The overall theme to Sanborn’s clues is that they are factual statements, but often they answer different questions than we thought we asked. Notice how Sanborn rarely uses our K(x) taxonomy when discussing “the last 97or 98″ characters. He deliberately toys with this ambiguity through his “K4 is standalone, but K5 requires 1-4″. Notice how we all assume, without support, that he is talking about K4 with the Berlin Clock. Hold that thought for a second, and notice another big Sanborn clue theme: “it’s not what it is, but rather where it is that’s important. Sanborn seems all too willing to offer ever longer cribs, as long as they are after position #63. We all know he is a master of illusion, and manipulating our perspective- he is after all, an artist, not a cryptographer, and a pretty good one. So’s Scheidt, (but in his case, we have an artistic cryptographer-the most dangerous kind)
The entire clue is get us to realize that K4 is a reflection of K1 in the water. K1 is 63 characters. If reassembling this reflection, K4 is also 63, and thus any characters after that may serve another, as yet undetermined purpose. So it now seems pretty clear that Sanborn thinks he can spot us the whole 35 character string beginning with BERLINCLOCK, and as long as he preserves the mystery of the 63, we’re not much better off.
So restated, the clue says: Before you are going to be able to use the clue in the context I intended, you will have to focus on the element that I placed right before the element I called attention to. I propose thinking of “K4″ as 63 + 34 or 35. Just throwing it out there and in my opinion there are some brilliant thinkers on this particular post of K-Fan’s.