I had a slightly different problem:
As a result, I resorted to float
to for the left and right columns, and could then use Bootstrap's row
to do the fluid columns in between.
<div>
<div class="pull-left" style="width:240px">Fixed 240px</div>
<div class="pull-right" style="width:120px">Fixed 120px</div>
<div style="margin-left:240px;margin-right:120px">
<div class="row" style="margin:0px">
Standard grid system content here
</div>
</div>
</div>