[exim] emulating $verify_mode

Hi,

I'm still searching rather unsuccessfully for a way to prevent my
router/filter from changing a counter when run in verify mode.

Is there any way of emulating the new variable $verify_mode in older
versions of exim? (I'm using v4.80 as provided in Debian Wheezy) Perhaps
by setting a variable in an acl which can be picked up in the filter?

I don't want to use no_verify on my router, since that means mail which
would have been be accepted aren't. I also don't want to turn of
recipient verification. The logic in the filter is fairly complicated
so I don't really want to duplicate it by implementing a non-mutating
version specifically for verify mode. However I might be able to
duplicate the router definition. Thus I thought about doing this and
checking the $router_name but alas that doesn't variable also doesn't
exist in the versions in question. And that is currently where I am
stuck. Maybe there's something else which allows my filter to detect
the context it is running in?

Thanks,

Nick