I've had the same trouble but finally found this: https://github.com/decioferreira/bootstrap-generators
It includes Bootstrap 3.1 and provides scaffolding and you can choose haml and scss as well as other options.
For example when I did rails g scaffold Link guid:string profile:string media_url:string
It automatically produced this:
EDIT FOR HEROKU USERS
I did have trouble pushing my app that is using bootstrap-generators (v3.1.1) to Heroku. Heroku was giving the error File to import not found or unreadable: bootstrap.scss
The fix turned out to be to modify the automatically generated bootstrap-generators.scss file. Change @import "bootstrap.scss";
to @import "bootstrap";
(eg just remove the extension).
NEW EDIT FOR HEROKU USERS
The new gem 3.1.1.1 fixes the bug. You no longer need to change @import "bootstrap.scss";
to @import "bootstrap";
in the bootstrap-geneerators.scss file.