[exim] Pass custom variable on to next router

Hi,

We're trying to setup some extra routers in our Debian exim4 config to check
for per-mailbox anti-spam settings. Some of these routers just check the
mySQL database for the customer setting in the "condition" and then add a
mail header so it is marked for later on. Then after several checks, the
mail is checked for these marks and should be acted on accordingly.

Now I've just found out that adding and removing headers isn't the way to
exchange information between routers because those are not effective until a
transport is reached.

How can I pass on information between routers so the next router can check
for something set in the previous router?

I'm looking for something like the $acl_m0 - $acl_m9 facility in the ACL but
then for use in routers.

Thanks for helping out on this!

Martijn