Change Bcc in reply-hook

Hi mutters,

I would like to set the From and the Bcc header in a reply-hook. My
relevant muttrc entries are:
reply-hook "%L group" source ~/.mutt/accounts/group
and in ~/.mutt/accounts/group:
set from = "a [ at ] a.a"
unmy_hdr Bcc:
my_hdr Bcc: $from

The From header is set correctly, but the Bcc isn't. In the manual I
found "that my_hdr commands which modify recipient headers, or the
message's subject, don't have any effect on the current message when
executed from a send-hook", and read somewhere that this also applies to
reply-hooks.

Is there any way to get arround this? Basically what I want to do is
move mails I send to both the inbox and another folder dependent on the
from address. Any ideas?

Cheers