hello
asgallant is right, you can't remove it with the API. But did you try and set the inactive regions to 'transparent' or 'none'?
what you can also do, is add some advanced CSS selectors like:
#visualization path {
stroke-width:0; /* to remove the borders */
}
and a more tricky one, would be find which shape is the US one, and apply something like:
#visualization path:nth-child(3) {
fill:#FFF; /*color shape white. alpha transparency css could be used also*/
}
this would probably not work in some older versions of IE... but I hope it helps!