I thought this self explanatory: however, I'll try to clarify:

The cellular radio has a 10.200.0.x/24static IP. We also have field equipment using 10.200.1.x and 10.200.2.x class C's.

The carrier routes traffic from 10.200.0.x to the other two blocks.

Now lets attach this radio to a router with, say 2 ethernet ports: the host network on FA0 with an address of 192.168.1.1/24, and the radio with an address of 10.200.0.1/24 on FA1, with the port set to acquire the address via DHCP. A console user can ping various radios on the 10.200.0 network; however, I need some way to indicate "if you want to talk to 10.200.1.1, ROUTE VIA 10.200.0.1". If I try this, IOS indicates "address is on the local router"

Nothing is self-explanatory unless you attach a network diagram comprising all device and addresses.

Anyway, your SP doesn't route anything else than 10.200.1.0, 10.200.2.0 and 10.200.3. That means if you want to use other addresses, you have to build your VPN. This is easily done with GRE tunnels, either point-to-multipoint or full-mesh point-to-point.

If you never did things like that before, I recommend you hire a networking professional for the job.

You misunderstand the question. WHile the SP will route traffic between the 3 10.x class Cs (e.g., a device attached to 10.200.1.1 can address 10.200.3.1), I need to be able to route LAN traffic from 192.168.1.1 TO ALL THREE CLASS C's.

Since I cannot make the port where the cell radio is attached the default route (which would solve the problem nicely and in fact works), is there some way to be able to set static routes for 10.200.1.2 and 10.200.1.3? I had thought that an overloaded NAT would work, but am not making any headway on this...