Low latency 9bit 485 data handling on a DUE

I am working on trying to get the DUE to sit on a bus pretending to be a vendors own device.

What I need is the DUE to handle 485 data, and respond within 2ms.

The UART seems ideal for this, with 485 and 9bit modes baked right in, but the serial library isn't so well suited.

I was thinking of just modifying the libraries to allow for the new modes, but while that may seem feasible, the guts for a 9bit mode would be a real kludge (like 2 bytes for every RX) and I still would have to poll the serial library to check for data availability.

Currently I am using a custom soft uart to evaluate the protocol, but it is RX only, so I haven't had to really worry about 485 TX mode.

I am considering allowing the serial library to initialize the registers, then slip in my own interrupt handlers and modify the mode bits.

Does this approach seem reasonable, or should I go the whole way and replace the serial library with my own?