[exim] receiving mail on exim behind a :25 port firewall ..

hello,
i would like to ask the community if there is anything i can do in the
following situation:

1. linux server at home, behind a small router connected via a pppoe
firewalled connection with dynamic allocated ip address (i can send
emails fine behind the router, but i cant receive, my :25 port is
firewalled by isp, that cannot change unfortunately.)

2. linux server hosted on a public static ip, full access on the
machine, exim configured and running there.

is there any way i can set up the two exims to be able ro receive mail
at home, on the firewalled linux ? i have full access on my domain dns
records aswell..

thanks!