If there were a way for the command being run on C2 to write its output to STDOUT, instead of creating a file on C2, then Net::SSH would be the only thing you need.

Net::SFTP will not work unless C2 is running an sftp server. In any case, I think that using Net::SCP from C1 will be more suitable, assuming you know the path and name of the file on C2 that you need to transfer to C1.