altering a pattern to make a buttonhole?

[ChroniclesofYarnia]

I am doing the technicolor cozy in stitch and bitch (except mine isn't techinicolored. :lol). In the instructions they have you sew velcro onto one side, and put a faux button on there. I would prefer to have a real button. How would I go about doing that? I only have one skein of my yarn...but can more than likely split it up with a little effort if that is what required.

Thanks!
Chris