I too thought about adapting the pattern for the larger size Moleskine. I haven't gotten around to doing anything about it yet, but these were my thoughts on how to approach it:
1) Measure the current pattern and determine the difference between the pattern pieces and the dimensions of the journal. Then create my own pattern and apply the same difference for the larger size journal.
2) I could use this free tutorial to help me figure out how to create my own journal pattern:
I can go do option #1 tomorrow and post the measurements for you. Do I think it's worth the money to pay for a pattern where you have to do some additional work (determining and figuring out your own pattern piece)? I don't really think so, especially if it's full price. On sale, maybe. What I do like about the pattern though are the numerous pictures that accompany the instructions. The instructions and pictures are useful for making any kind of lined bag. It would have been nice if other sizes were included.
I think it's not a bad idea to try option #2 first since it's free.
Please post pics if you make the journal clutch! HTH