No, sorry, no changable numbers
Considering you've only driven 2000 miles in 3 months, it will probably be a while before your average shoots to 65 MPG. Even now, in fact, you're just at 55. I think you'll be fine with 60 MPG, really. At this rate it will STILL take you 4-6 months to start averaging that!
Also, don't forget, there are matching t-shirts as well.