i (and etokyopop) opened my boat by drawing with a pencil and ruler leaving 1/2 inch between the "dip" (where the cover sits in) and where i was cutting just to give it a bit of strength, but you honestly dont need much space there. i like the extra strength from that as opposed to leaving just 1/4 inch or so.

i then just used an exacto knife and scored each cut making sure it was straight, and then with medium pressure just keep going over the same cut (evenly across all sides) until the knife cuts through. with a sharp knife you dont need much pressure and 3-4 passes will get a cut through. leaves no plastic residue like a dremel, and gets a super-straight and clean cut