selective --throw-keyid?

[sen_ml at eccosys.com]

hello-

  is it possible in theory to create a message in which --throw-keyid
applies to particular keys only (and have this be useful)?  the
documentation for --throw-keyid says:

       --throw-keyid
                 Do  not  put  the  keyid into encrypted packets.
                 This option hides the receiver  of  the  message
                 and  is  a countermeasure against traffic analy­
                 sis.  It may slow down  the  decryption  process
                 because all available secret keys are tried.

  what i would like is to be able to have some keyids appears in
encrypted packets and other keyids to not appear.  the idea being that
some recipients use gnupg (so decrypting messages created w/
--throw-keyid is possible) and others use pgp (so decrypting messages
created w/ --throw-keyid is not possible -- well, at least it didn't
work when i tested it).

  does this idea make any sense, and if so, how hard would it be to
implement?