To be honest, I doubt this will be implemented in scp. As
http://www.openssh.org/faq.html#2.10 says:
2.10 - Will you add [foo] to scp?
Short Answer: no.
Long Answer: scp is not standardized. The closest thing it has to a
specification is "what rcp does". Since the same command is used on
both ends of the connection, adding features or options risks breaking
interoperability with other implementations.
New features are more likely in sftp, since the protocol is
standardized (well, a draft standard), extensible, and the client and
server are decoupled.