Add message to model validation errors

Hi!

I'm using CAPTCHA plugin (http://github.com/zendesk/captcha/tree).
When CAPTCHA validation fails the error message is added to
flash["error"].

How can I add the CAPTCHA error message to the model validation
messages? Also I would like the CAPTCHA text field to be wrapped in
<div class="fieldWithErrors">.

TIA!
/Erik