From my reading, it looks like the Forefront TMG will not allow the passing of RDP
connections through the firewall without configuring a non-standard
port for each IP address of the internal servers and clients.
Well, from my reading of your question it looks like you dont know how to use RDP, at least the current iteration ;) I happily connect to whatever server I want behind my TMG without configuring a port per server.
TMG supports what has been standard in windows - a gateway server.
That pretty much means that your remote desktop client connects to the gateway server (using HTTP, btw.), then the calls get forwarded from there to the final server internally.
This is a standard setting in the remote desktop client where you can enter the gateway host address (url) which most administrators do not know because of not bothering to read the documentation.
explains what a Terminal Services Gateway is and how it works in general.
has some explanations how to set things up for TMG. This one creates a web site for connecting.
it reaslly is quite easy to set up. And using HTTP as carrier protocol for RDP has the serios advantage of being able to work quite often when normal TCP forwarding is disabled or limited by firewall rules ;)
talks of publishing TS Gateways directly ;)