Possiblt to bridge a HTTP file GET to a multi-part file POST?

Possiblt to bridge a HTTP file GET to a multi-part file POST?

I'm not sure if this is possible, but:
I have a server A that will accept files via a multi-part POST. I have a
server B from which files can be obtained via a GET request.
While obviously, I can transfer a file by downloading from B, then
uploading to A, is there any way I can somehow 'bridge' the requests, such
that I can transfer a file from B to A, without it having to pass through
a third machine i.e. B uploads directly to A.