[Exim] Hiding originatin IP?

My superiors wants me to investigate the possibility of "masking" all IP's
from sending hosts within our intranet.. Or replace them with a hash of the
IP. As in, they do not want the RFC 1918 IP of the sending system to be
viewable in the headers. Or, as i said, hash it. (exim 4.x)

Can this be done?
Would it violate any RFC?
(Personally i dont see the point, but hey, if boss-man say check this, i
check).