What are the reasons you want Ubuntu? By any chance is it due to codecs and such licenses? You can quite easily get all of that working in Fedora or Debian.
I may have overlooked something, but one of the bigger reasons to want ubuntu, may be codecs and ability to play videos? I'll go ahead and take a guess that it might be partly codec related, though I may be guessing wrong.
For example an easy fix to make Fedora play almost any modern video --> clone your fedora template --> Add RPMFusion to your new fedora clone template. Install ffmpeg and vlc from RPMFusion repositories (Qubes has a really easy and quick guide to enable them). Voila, you can now watch HTML5 content videos in firefox on AppVM's based on your fedora template clone. Verify if it works with
www.youtube.com/html5
For protected content, such as copyright protection, which can mess up an otherwise working HTML5 video, you'll probably need the google browser either way, directly from googles website. Unfortunately it can be messy to get protected content to play in browsers like Firefox. But that should apply to Ubuntu as well.