As a quick fix you could create a m83.5 channel using the channel calculator. This could then be set to 0 so that you can use the DRS. The channel calculator is in Tools -> Calculator.
I would set it up like this:
m88 is the name of one of your other input channels.
At that point you should be able to see your new channel in the Channels Browser, but the DRS won't be able to find the channel until you set its Mass property. You can do that with this one line:
If you copy and paste that line into iolite's python console (Tools -> Python Console). You should have a m83.5 channel that is filled with 0, and has a Mass property of 83.5.
Obviously, this is just a stop gap measure for testing 😃
If that doesn't work, please just let me know.