You can also give them DHCP leases that don't set the gateway. That's usually a good idea anyway, and it's pretty easy to do if you use something like dnsmasq.

You can also give them DHCP leases that don't set the gateway. That's usually a good idea anyway, and it's pretty easy to do if you use something like dnsmasq. On my config I have an IP range on my subnet that is the default one and doesn't set the gateway. When I 'trust' the device I add it's MAC to the list of trusted ones.