this will take quite a bit of custom coding to accomplish, We could help implement this in a premiere support appointment.
The basic Idea is this:
We have custom markup tags that we support, for a quote the tag is:
[ quote by="name"]quote goes here[ /quote]
(i added a space to the quote tags to prevent the translator from treating them as a quote)
We then write a php function that acts as a translator to convert the custom mark up to HTML markup:
<div class="quote"><h2>by: name</h2>quote goes here</div>
to get the quote we store the username and text from the original post into a hidden field and when someone checks the quote option we move it into the textarea using the pre-defined markup as described above.