Not currently possible.
The only way to do this would be to create a new 'quote' that has no pricing information. Literally just a header section and the video.
Alternatively, create the video and save the link to a custom field. Then use an email template to give the client the link. All that you're doing in QW is adding the link and creating an email - of course, this way the link directs them straight to YouTube, but is going to much quicker and cleaner.