[exim] Setting name used in EHLO/HELO

Hi,

Sorry for this strange question but I need to set the name used as
EHLO/HELO paramaeter by my exim4 box because the fqdn of the box cannot
be looked up on the Internet, being part of a private network (behind a
firewall), and I'm not able to change the fqdn without breaking
kerberos. Unfortunately recently I had to send some e-mails to a site
which quite stupidly checks the name used as the EHLO/HELO value :-( .
Could you tell me how could I change the name used as EHLO/HELO
parameter in my Exim 4.6.3 (debian).

T.I.A

Geza