Without some form of proxy (which is what Sygate is), no, it can't be done. The reason is that you have only one WAN (external) address and this has to be translated, or routed, in to multiple different LAN (internal) addresses.
TCP/IP is just a protocol that transports the packets. Unless you have some way to convert from WAN to LAN, the packets can't get out or in. DHCP is just the dynamic server that assigns the IP addresses. What you need is NAT (Network Address Translation).
Russ, NCNE