This is entirely possible with Singularity!
To pull the element out of its container just use a negative margin. But proper width and margin sizes require some tricky math:
<div id=container>
<div id=a>a</div>
<div id=b>b</div>
<div id=c>c</div>
</div>
$grids: 1 2 2
$gutters: .25
#container
+grid-span(2,2)
#b
$coefficient: (1 + 2 + 2) / (2 + 2)
$width: column-span(1, 1) * $coefficient
$gutter: gutter-span() * $coefficient
width: $width
margin-left: 0 - $width - $gutter
float: left
clear: both
+layout(2 2)
#a, #c
+grid-span(2, 1)
Result:
Demo: http://sassbin.com/gist/6953993/
Note that the width and position of the pulled column do not match the grid perfectly. This might be due to rounding errors in browsers, or my math might be wrong.