Setting DISPLAY on the screen shell

[JCA]

  When I establish a connection by means of ssh, from a host A to a
host B, I can use the output from the 'who am i' command in B so that
in the shell created in B by the connection, the DISPLAY variable is
set so that the output from X commands in B is sent to A. Indeed, a
typical output from 'who am i' invoked in the shell in B would be

   UserName      pts/13       Aug  4 11:01 (A.domain.org)

where A.domain.org is Internet name of A.

  Now if the shell in B is created by screen (A is starting the
connection by means of ssh, which in turn launches screen on B) then
the output from 'who am i' in this shell would be

  UserName      pts/13       Aug  4 11:01 (:pts/2:S.0)

  That is, the information having to do with the host establishing the
connection is not there anymore :-( I thought that one could encode
such data by means of the -S option to screen, but the problem is
that, once the shell created under screen is up and running, I do not
know how to retrieve that information. screen -list does give access
to it all right, but it is not useful when more than just one screen
session is running in B, I think.

  Any ideas?