[Exim] ISP has blocked incoming port 25

Hi,

My isp has blocked incoming connections on port 25, but as a work around, I
want to
get a friend of mine's server (running exim 3.X) to become the primary MX
record
for my domain, then get that to forward the mail to me on a custom port (say
22225).

I've read through the FAQ, Specs, googled.. I can't find anything!! (or
maybe it's just
me)

Anybody managed to do this before? Or have any suggestions as to how?


Thanks!

Andrew