How can we improve WHMCS?

The initial problem is due to clients registering with domain mail hosted by their old host, although this is not best practice a lot of them do it:

Is it possible to set the provisioning module to setup the DNS zone to use remote mail servers when the client selects "use existing domain" the reason I ask is because it currently sets up the account and DNS zone to use local mail then the automated account login details and verification mail does not send out to the domain successfully I then have to manually set the DNS zone to remote mail and resend the login details and verification mail to the client. Generally clients will arrange/schedule a time to change the name servers to ours but until they do that how can I provision the account to use remote mail by default when "use existing domain" is selected?