Pfitz base building past 60 miles per week

I recently bought Pfitz's Faster Road Racing book and like the base building schedule. I realize that a schedule for base building isn't necessary, but I like the structure.

Does any one have ideas on the best way to extend the schedule past 60 miles per week? It would be great to hear ideas on the best way to get from 60 to 75 miles per week using Pete's framework. Thanks.