[exim] Logging to mainlog from system filter

Hello,

Is it possible to write to the exim mainlog from a system filter ?

If possible, I would like to do something like : warn text "Some
message"

I'm trying to achieve exactly the same as :
http://lists.exim.org/lurker/message/20060619.102901.e58c865c.en.html -
but I didn't find any solutions to this request.

Many thanks in advance,

Paul