I believe that most if not all drives will not allow you to bypass c1/c2 error correction.
You can get the raw rf signal by attaching an oscilliscope to the drive before the demodulator/decoder. Most drives have the demodulator and decoder built into the same chip so you will probably also have to write software to demodulate the raw RF signal, then you will have the raw demodulated F3 frames (before error correction) which is what I think you are looking for.
On the other hand it seems like you could just write software that does the CIRC encoding (which will also give you what you want) along with the software to do the error correction and decoding.
Someone else out there might have a more simple solution.