A CSS fix is probably simpler:
http://jsfiddle.net/isherwood/LtzZz/4/
.accordion span.opener {
display: block;
width: 100%;
background-position: right 50%;
}
You'll want to wrap that in an appropriate media query so it only applies to the mobile menu.
Correction: Just use the .mobile
class to filter it:
.mobile .accordion span.opener {
display: block;
width: 100%;
background-position: right 50%;
}