Just go to "reply with quote" as usual, then have a look at the tags surrounding the quote. You can copy and paste them to divide up the quote into sections, or select and delete parts you don't need.
how to do this
Right.
A related trick is, to quote from multiple people:
Set up one quoting-Reply (trimming it or not). But instead of clicking the Post button, select and copy your complete post (quote-tags and all), and Cancel the post.
Then start a Reply off of the other quote and paste your original quote-post material into that. Rinse and repeat if needed (hopefully not too much), before Posting the total.