Steps to disable page responsiveness
Omit the viewport <meta> mentioned in the CSS docs
Override the width on the .container for each grid tier with a single width, for example width: 970px !important; Be sure that this comes after the default Bootstrap CSS. You can optionally avoid the !important with media queries or some selector-fu.
If using navbars, remove all navbar collapsing and expanding behavior.
For grid layouts, use .col-xs-* classes in addition to, or in place of, the medium/large ones. Don't worry, the extra-small device grid scales to all resolutions.