[exim] Redirect route data variable expansion

I have to following redirect router:

list_redirect:
driver = redirect
domains = example.com
senders = a@??? : b@???: c@???
local_parts = list
data = a@???, b@???, c@???
errors_to = a@???
headers_add = List-Id: <list@???>

Everything seems to work so far except that I was not able to filter
addresses from the CC header in data. My idea was something like this:

${filter{a@???, b@???, c@???}{and {{def:h_Cc}}{{!eq{$item}{$h_Cc}}}}}

Except for the fact that the first argument is not a list, because it
doesn't use : as separator, I got the following error:

missing } at end of condition inside "and" group inside "filter" item

My guess is that $h_Cc isn't expanded. Any further ideas?

Regards,
Matthias-Christian