I think in this case then, if at all possible in terms of time and work involved, I would personally noindex the paginated pages, but look through them (or get email updates with the comments), and copy the good comments and put them on the main page.
(it won't be duplicate / think / useless content in google's mind if the other pages are noindexed, right?)
sort of like: This is what people are saying about this important cause, followed by comment highlights, on the main page under the description.
Might be too labor intensive depending on how many signatures and comments you get though...
Just a thought.