[Exim] IPv4 only smarthost

I'd like to detect whether a host I'm sending mail to has an IPv4
or IPv6 MX record. If it's Ipv4, I need to send it to a local
smarthost (this is obviously easy enough), but if it's IPv6 I
want to deliver it myself directly.

In case I don't need to write a patch for this, is there any way
I do this using existing configuration commands?

I'm using exim 4.30 :)

--
Colm MacCárthaigh  /  HEAnet, Teach Brooklawn,  / Innealtóir Ghréasáin
+353 1 6609040    / Bóthar Shelbourne, BÁC, IE /   http://www.hea.net/