This gets mentioned regularly, figured I'd throw my two cents in since I have done it. I put larger tires on a lifted Quigley last year, and had some rubbing over bumps while in corners (the normal time).
I chatted with Ramsey, and he gave me the two minute rundown of what Agile had done in the past, so I set to work.
Step 1: Remove fenders entirely from the van. This might not be necessary, but it only takes 5 or 10 minutes, and makes the whole process a lot easier.
Step 2: Draw a nice 'pizza slice' on the fender, then cut it out: