Special Setup for Mega's Extra Serial Ports

I need to set up two of the Mega's additional serial ports to receive 9-bit data. Are there any library functions I can use for this, or will I need to write custom code to set up the ATmega1280's USART control registers?

If the latter, are there any examples of register-level programming that might be useful?

I don't believe any of the existing Arduino hardware or software serial supports using 9 data bits. However the data sheet for the mega1280 does show how one would go about it. Here is an extract:

22.5.2 Sending Frames with 9 Data Bit If 9-bit characters are used (UCSZn = 7), the ninth bit must be written to the TXB8 bit in UCSRnB before the low byte of the character is written to UDRn. The following code examples show a transmit function that handles 9-bit characters. For the assembly code, the data to be sent is assumed to be stored in registers R17:R16.