Rather than editing the files to produce the unmodulated version. Why not do it with hardware! I believe there is a fairly large difference in frequency content between the code and the carrier frequency. Because of this, the task could likely be done with a single pole filter, consisting of a simple RC circuit.
For info:
[Link: en.wikipedia.org]I'm not sure of the frequencies involved off the top of my head, so feel free to send me some info, and I'll help you pick some components. It should be cheap and easy to build.
I would start by choosing the cutoff frequency two decades below the carrier frequency. This would attenuate the carrier by 40dB. (Since an RC filter is 20dB per decade.) For example, if the carrier is 800KHz: Two decades below would be arrived at by dividing by 100. This results in us choosing a corner frequency of 8KHz.
The series resistance poses some questions. We need to know what the input inpedance is on the Control S jack. Anybody know? If it is fairly high, then our choice of R can also be fairly high, allowing us to use relatively small values for C. And smaller values for C are less expensive, easier to find, and physically smaller.
For example, if the input impedance of the Control S jack is 1Kohms (1000 ohms), we would want the R, of the RC filter to be about 1/4 of that or less. If we chose the R to be 1/4th, then the signal coming in will be attenuated by only 20% or 1/5th. This is calculated by:
attenuation in % = Series R / ( Series R + Control S input impedance )
Last we would choose C using a form of the Fc equation from the Wikipedia reference. Specifically: C = 1/(2*Pi*R*Fc), where Fc is the corner frequency we chose in the first step, and R is the series R we chose as about 1/4 of the Control S jack input impedance.
Anyone who knows the input impedance of the Control S jack or can measure one, and the modulation frequency, let me know the info, and I'll go through a couple quick calculations to pick a couple components that should be inexpensive, easily available (although the easiest place to get them may be .... you guessed: Radio Shack), and simple to assemble.