I use a fantastic replication/sync called Allway Sync that can do this.

I also know that some people back up to a local or at least LAN destination first in order to get the backup done quickly (and possibly retain a copy locally) and then use another application to replicate that backup to the cloud. I know FTP support has been requested for a while. You’d have to ask them, and/or create a Wish List thread. If that's not possible for your use case, you might find that drive letters are not a viable alternative. This is all why the best practice is to access network paths by UNC paths rather than mapped drive letters. And I believe (but am not completely certain) that even if you were to reconfigure Reflect to run scheduled tasks under the logged-on user's credentials, the background execution would still occur under a different context and therefore not have access to that drive letter mapping, even with that workaround applied. However, Reflect jobs that run in the background as scheduled tasks run under the SYSTEM account by default, and that context would NOT have access to mapped drive letters created in the context of the logged-on user.

If a mapped drive letter is created in the context of the logged-on user, then after applying that workaround, things will be fine for Reflect jobs that are manually launched in that user context, such as by right-clicking a definition file and selecting Run Now, because that job will run in the user's context and therefore have access to that mapping. This is documented in this KB article, and as you'll see, there is a workaround available for that issue. First, drive letter mappings are specific to individual user sessions, but by default Windows does not make mapped drives created in the standard user context available to applications running with elevated privileges, even when those elevated applications are also running under the same user context. The reason I say that is that if this tool just maps a drive letter as opposed to exposing AWS through an actual UNC path, that's unlikely to be a viable solution for a few reasons. If that other tool is expensive, make sure that you test it both when running backup jobs interactively within the user session and when running them in the background as scheduled tasks, assuming the latter is something you'll want to do in your use case.

Macrium reflect cloud backup