I appreciate a lot that I can assign a bug to two packages at a time
(where either of the packages can close the bug). However,
submit@bugs.debian.org does not seem to understand a pseudo-header like

Version: kjscmd/4:3.5.10-1,kdelibs-data/4:3.5.10.dfsg.1-2

See for instance

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=520453

I had to issue two "bts found ..." in order to make the bts understand
the two versions.

It's not exactly as requested, but you should be able to achieve the
requested result by using appropriate "Control: found" pseudo-headers
in the mail to submit@.

Regards,

Adam