[exim] shell commands in exim.conf macros?

hi all,

is it possible to expand a shell command in an exim.conf macro?

e.g., this, of course, works

     MY_HOSTNAME         = mybox.mydomain.com
     MY_DNS              = 10.0.0.6
     MY_IP               = 10.0.0.5
     local_interfaces    = MY_IP : 127.0.0.1 : ::::1

-->
2005-09-01 22:16:42 exim 4.53 daemon started: pid=23959, -q30m, listening for
SMTP on [172.30.11.5]:25 [127.0.0.1]:25 [::1]:25

but this, with the "dig" cmd
     MY_HOSTNAME         = mybox.mydomain.com
     MY_DNS              = 10.0.0.6
     MY_IP               = `dig +short @MY_DNS MY_HOSTNAME`
     local_interfaces    = MY_IP : 127.0.0.1 : ::::1

results on exim launch in:

-->
2005-09-01 22:17:37 Malformed IP address "`dig +short @10.0.0.6
mybox.mydomain.com`" in local_interfaces


i'm reading through "the book", but -- if it's in here -- have missed it ...

pointers?

richard