Well, that's fine if you can use the pinChange interrupt, but not if you require the use of the external interrupt
I modified my shield, it was no problem, and the code was trivial to change because you nicely defined the pin numbers in one place.
I'm not sure what's so bad about vias - after all, all of the component holes are through-plated, so it's not as if you're avoiding the need for that plating when the boards are made. Looking at the layout, you could just shuffle all the pins along two places though, without needing any vias (you might need to move the header sockets over slightly to make enough room). Just a suggestion anyway - mine's working how I need it. Thanks for a nice product!