Tell LMTP who is original recipient?

[MRob]

For some time it is possible to make postfix virtual tell a LDA who is 
the original recipient, add x-original-to header. But not LMTP. This 
create problems in final delivery, one example is autoreply vacation 
program cannot check if message was addressed directly to this user or 
not, so many autoreplyies are sent when it should not happen.

Feature request for this seems stalled, but in meantime, is there any 
workaround?

FYI, I use dovecot LMTP.