I'm currently trying to fix this problem as well, and am seeing mentions of hosting a cran-like repo on S3, but not seeing any detailed examples. should it be as simple as taking the advice from here, but then duplicating the contents to S3 after it's created, or is it more involved than that?
A slight wrinkle is that many examples are using private github, and our business uses bitbucket exclusively, and I'm not sure how that would effect the tooling etc.