The default grid system will be come fluid (using percents for widths), so you'll have to just find and replace the row classes and you should be okay. Unsure about more complex layouts though.

This is awesome, thanks for the clarification.

I got scared at 'dropping fluid', because it's become been pretty clear to me that the fluid approach in bootstrap was better for most apps, and I was wondering why in fact using the fluid approach wasn't more popular. I got worried that you were making it much more difficult -- but it turns out you agree with me, and instead are making it the out of the box default! woo!