Hi Josh,
I have heard what you are talking called "extended composite" before and it was looked at but never supported by any of our parts. I think you'd probably need to use a sufficiently high speed A/D and then a DSP or FPGA to implement the decode. We make lots of high speed A/Ds though I'm not an expert on which one would be best. I imagine one of our Blackfins or Sharcs could decode the digital signal. I haven't heard of anyone doing this though so I'm not sure what else to suggest.
Dave