Can’t you just mirror the files somewhere else and then do a createrepo?
I have a similar problem with the Zimbra repository that lives on AWS and needs s3-cmd to be downloaded.
I do that somewhere, export it via nginx and sync from that location.
I know it’s a bit silly, and I wish all this crazy crap would just stop and they’d just build “normal” repos - but this might be one of the cases where going the path of least resistance is just the best…