Hi , If you have a Seeeduino , you can use it to program the Rainbowduino without UartSB. The Rainbowduino also have the ISP interface and you can pragram it like a AVR SCM, but when you do this the Arduino bootloader will be covered and you must download the bootloader again if you want to program it through ArduinoIDE with any tool.
you could also use the avrisp code in the mega-isp project on google code.
i did this and compiled the sketch for the rainbowduino in the ide, then took the hex file and uploaded it using avrdude.
i have not tried the route that freezing is talking about, but it seems a little easier. I will give it a shot tonight.
Miles also has a way to get it going, which sounds kind of like the way that freezing is talking about, only without needing a board that has a removable chip.
you can read through some of the discussion in this topic