"use a Triscend derivate and configure the number of uarts that you need"

You beat me to it!

See the end of the following thread on the Keil forum for my estimate of how many UARTs you might fit onto an E520:
http://www.keil.com/discuss/docs/thread1868.htm
Note that I consider only the full UART SoftModule, where each one includes its own baud rate generator.
If some/all your UARTs will run at the same speed, you could use "Half" UARTs and save some logic by sharing baud rate generators.
And if you only need a single direction on some ports, you can save even more by only implementing the required part (receive or transmit).

That's the beauty of CSoC!

See the list of supplied SoftModules here:
http://www.triscend.com/developmenttools/fc_softmodules.htm