How can I configure dhcpd to only update the reverse zone in bind?

I've got dhcpd pushing updates to bind, and it seems to be working fine:

named[24161]: client 192.168.10.1#59141: signer "dhcp_updater" approved
named[24161]: client 192.168.10.1#59141: updating zone 'office.lan/IN': adding an RR at 'Examples-MBP.office.lan' A
named[24161]: client 192.168.10.1#59141: updating zone 'office.lan/IN': adding an RR at 'Examples-MBP.office.lan' TXT
named[24161]: client 192.168.10.1#47923: signer "dhcp_updater" approved
named[24161]: client 192.168.10.1#47923: updating zone '10.168.192.in-addr.arpa/IN': deleting rrset at '7.10.168.192.in-addr.arpa' PTR
named[24161]: client 192.168.10.1#47923: updating zone '10.168.192.in-addr.arpa/IN': adding an RR at '7.10.168.192.in-addr.arpa' PTR

However, our MacBooks are often on WiFi and plugged in via ethernet at the same time. This means that bind rejects the update, because of duplicate hostnames:

named[24161]: client 192.168.10.1#34165: updating zone 'office.lan/IN': update unsuccessful: Examples-MBP.office.lan: 'name not in use' prerequisite not satisfied (YXDOMAIN)
named[24161]: client 192.168.10.1#35832: updating zone 'office.lan/IN': update unsuccessful: Examples-MBP.office.lan/TXT: 'RRset exists (value dependent)' prerequisite not satisfied (NXRRSET)

I don't actually care too much about the forward lookup, I just want the reverse lookup on both IPs, so that both IP addresses point to the same hostname.

Here's the relevant part of dhcpd.conf:

ddns-update-style interim;
ddns-domainname "office.lan.";
ddns-rev-domainname "in-addr.arpa";
key DHCP_UPDATER { algorithm hmac-md5; secret "{{secret key}}"; };
zone 10.168.192.in-addr.arpa. { primary 192.168.10.2; key DHCP_UPDATER; }
zone office.lan. { primary 192.168.10.2; key DHCP_UPDATER; }

and the relevant parts of named.conf.local:

zone "office.lan" IN {
    type master;
    file "/var/lib/bind/office.lan.db";
    allow-update { key DHCP_UPDATER; };
};

zone "10.168.192.in-addr.arpa" {
    type master;
    file "/var/lib/bind/10.168.192.in-addr.arpa";
    allow-update { key DHCP_UPDATER; };
};

I tried commenting out the zone office.lan. and ddns-domainname lines in dhcpd.conf, but then I was just getting these error messages:

dhcpd: Unable to add forward map from Examples-MBP.office.lan. to 192.168.10.7: timed out

So the question is: How can I get dhcpd to just update the records in 10.168.192.in-addr.arpa, and not worry about duplicate hostnames in office.lan.db? Alternatively, is there some way to ignore duplicate hostnames, or alter the hostnames to make them unique?

Please let me know if you need any further information.