For the record:
- Looks like the latest dnsmasq in git does support dhcp-match: https://github.com/openwrt/openwrt/blob/master/package/network/services/dnsmasq/files/dnsmasq.init#L306, but it could take couple more years to get to our devices.
- /etc/dnsmasq.conf (which is not autogenerated) is included into /var/etc/dnsmasq.conf and adding following in it did the job for me:
dhcp-match=set:ipxe,77,“iPXE”
dhcp-boot=tag:!ipxe,ipxe.efi,ipxe,192.168.1.2
dhcp-boot=http://192.168.1.2/default.ipxe
(It points to a server 192.168.1.2 for loading ipxe.efi via tftp and ipxe config via http, but you can use your router for that if needed).