That's actually a much better sounding idea than just fragmenting the source into a whole new project, that will probably eventually suffer from disregard as Bootstrap continues to flourish.

In fact... https://github.com/twitter/bootstrap/wiki/Contributing-to-Bo...

There are variables for @baseBorderRadius, etc. They don't hit all of the spots yet, but it's getting there with each new version of Bootstrap.

boottheme.com does a good job. It's a 'wysiwyg' editor of the bootstrap less variables, and that includes border-radius.