Inviting a likely reviewer of a rejected manuscript as a co-author Researcher X is well known in area Y for the past five years. He finished his PhD about 4 years ago and now has over 1600 citations. In area Y, he has been the first author of all published survey and tutorial articles. Now someone (researcher A) writes a survey on area Y, narrowed down to a particular aspect in the same journals where Researcher X publishes. He submits his paper and got a rejection. Thus, A thinks the paper would highly benefit from researcher X's experience. The problem is there are strong indications that Researcher X is a reviewer of A's paper. Since A would like to resubmit to this journal, how could he write a convincing letter to Researcher X inviting him for co-authorship. For instance, does this look fine enough?

Dear Researcher X,

I am writing you with respect to my manuscript titled: 'My Title'. I will like to add more value to this paper to meet reputable journal G's standard. It is pertinent that I mention that the paper has been previously rejected from this journal with an opportunity for resubmission. I am thus requesting your assistance and co-authorship to improve on the quality of this manuscript.

I anticipate your response
Two points.


It's actually irrelevant, if X was the reviewer of the paper or not. If you want to ask them, do it. It does not matter, if X knows the paper already or not, but assume they don't.
I would appeal more to the professional interests of X in the mail. Like, "this paper focuses on the weight distribution of spherical cows in vacuum. My coauthors and I think the paper might benefit from your expertise on spherical horses in low gravity".