In the definitions below, $FQDN represents the Fully-Qualified Domain Name (FQDN) requested in the certificate subject, $DOMAIN represents the Registered Domain Name portion of the FQDN, and ${FQDN-n} is the FQDN with the first n labels pruned.
Calculate the MD5 and SHA1 hashes of the DER encoding of the CSR that will be sent to Comodo. Let these be $CSRMD5 and $CSRSHA1 respectively.
If requesting a non-wildcard FQDN, create the following record:
$CSRMD5.$FQDN. IN CNAME $CSRSHA1.comodoca.com.