Pccc decoder combo requires the modulation as a parameter because
it needs to evaluate soft decisions from the noisy complex QPSK signal that it receives.
In that sense, it is NOT doing demodulation, as it is not supposed to...
I don't know what the OFDM demodulator does, but if there is a way to get the
frequency/phase corrected QPSK signal out of it then you can feed it to
the pccc decoder (with appropriate "scaling" parameter) and perform decoding.
Achilleas