Ken;
I am a noob

and do not know how to solve your problem within SME Server.
However I am vpn'ing people into my home server with dedicated ip addresses (not a common internal ip for everyone but everyone with a dedicated internal ip) using the following contrib.
I relied on the following:
[ANNOUNCE] smeserver-openvpn-bridge-fws-1.0-3.rpm (stable).
It operates completely within the SME server control panel. It requires your clients to be Windows xp pro, xp home, or 2000. I have made it work with all of these. It is supposed to be good with apple and linux but I don't have that problem (opportunity?).
Hope I understood your problem, let me know how it goes.
Ian