Use gutter removed from a column into witdh of another column - Susy

See below:

Please click here to see the image, with the question http://imgr.es/26LP

I cant add the gutter with padding, because I'm using Paul Irish global box sizing.

Follows my code:

    $susy: (
        columns: 12,
        gutters: 18/81,
        global-box-sizing: border-box,
        debug: (
            image: show,
        ),
   );

   .container-selector-sample {
       @include container(1170px);
   }

   .column-selector-sample {
       @include span(2);
       @include breakpoint(mobile){
           @include span(12);
       }
   }

   .column-selector-sample {
       @include span(3);
       @include breakpoint(mobile){
           @include span(12);
       }
   }

   .column-selector-sample {
       @include span(7);
       @include breakpoint(mobile){
           @include span(12);
       }

   .column-selector-sample,
   .column-selector-sample {
       @include last;       
   }

Susy has a keyword for that! See the documentation for narrow, wide, and wider. In this case, you want to use wide:

@include span(3 wide);