For anybody who finds this page: DHCP-snooping can be enabled on its own, without a workaround, as of 17.1R1.
Starting in Junos OS Release 17.1R1, you can configure DHCP snooping or DHCPv6 snooping on a VLAN without enabling other port security features by configuring the dhcp-security CLI statement at the [edit vlans vlan-name forwarding-options dhcp-security].