Download manager is just another name for the prefetch or download command in action script.
Almost every Fixlet uses this to get files down from the root server.
The action to upload happens on computer A, the file move on computer B (root server) and the subsequent download on computer C, so a baseline will not work, but server automation might.
For the middle part, moving the files on the BigFix root server
\BigFix Enterprise\BES Server\UploadManagerData\BufferDir\sha1\#\########
\BigFix Enterprise\BES Server\wwwrootbes\Uploads
Maybe… Repeating action targeting BigFix server that a) uses xcopy with recursion to copy the new file in the Upload manager area into the wwrootbes area along with a naming convention to make them unique in the wwwrootbes area… b) in the same action, use relevance to calculate the sha256 and size and generate the full URL that would be needed in your subsequent download command… and then, c) action performs a REST API call to generate a custom action on ComputerB, passing the calculated prefetch command…
(As Jason mentioned, complex, overengineered, time consuming)