it's probably possible. I haven't needed to do this so I don't have a solution. The closest I've come is providing links to documents that are in the project. The tough part is that our projects often have multiple documents (so multiple links show up in the column, which is fine as long as you want to see all of those, and if you don't well... pull out your if/then statements).
I do your standard call on a collection of documents of course. You could try the same thing with a collection of proofs. I see the syntax for a proof URL is something along the lines of https://<your domain>.my.workfront.com/document/<big long guid looking thing>/proof/<shorter number>/view/ , so you would basically concat something that looks like this as your valueexpression, and sub in whatever those IDs are when you get to that part.
So once you find out what the two strings are (doc id? doc version id? proof id?) you should be in pretty good shape. And to do this, it's basically guesswork. Run a proof report and pull in any ID fields you can lay your hands on, and then open a proof and see which numbers line up to which fields. Honestly though, if you get stuck, just tell your users to use the document link and open the proof when they get there.
