I know we ruled out using a petition site, but I quite like the look of this -
http://www.thepetitionsite.com/takeaction/994415686
It has an image, a text, then a sample of the letter that will be sent. I also like the graphic for the number of signatures so far/and target.
There are no ads, and it has a little digg icon so each signee can recommend the page or email to others.
The simplicity of this petition page combined with a more detailed and personalized facebook page (which could be referenced on the petition) would still be another option.
I don't mean to put a spanner in the works by re-suggesting this - but for speed in getting the thing going, this could work better.
Shout me down if you like!! Just thought it worth mentioning again.