Is there some way to override BLACKLISTS on a per-host basis?

I'm still running a setup at home with a front-end relay server accepting mails for my domain and relaying copies to my Courier server (now up to 0.47.0!) on another machine (straight port 25 transfers with no authentication, obviously).

The trouble is, the front-end relay server has a quasi-dynamic IP from Comcast, so if I try to use (lines broken for clarity)

BLACKLISTS='-block=dnsbl.sorbs.net,BLOCK \ -block=sbl-xbl.spamhaus.org,BLOCK \ -block=bl.spamcop.net,BLOCK'

to shoo away other random connections to the back-end server, Courier gets a hit in the SORBS lookup on my incoming relayed mails and it rejects them. I thought I could override this on a per-host basis by having the IP address of the front-end relay server listed in courier/etc/smtpaccess/default (which has

allow,RELAYCLIENT,BOFHCHECKDNS=0

in the entry for the relay server's IP address), but that doesn't seem to override the BLACKLISTS checking.