The $10 off is already there when you go to order. They set the price at $29 instead of $39 for the first week.
Unfortunately, there's no way to pre-order. Lots of us just wanted to 'subscribe' when the series started but it's beyond Cafe Press' capabilities given how the POD model works. I asked about it a while back and CP can't assign a product number until the manuscript is actually uploaded (if I understood correctly).