Take a look at the Commander Speakermic. It has programmable feature-buttons for such features, as well as volume control. They're getting really cheap on eBay. Or at least they were. You can then debug/trace from there.
If you're interested in controlling other features of the radio as well, you might look into doing it with SB9600 using a small microcontroller, like ATTiny or PIC or such. If it's for something simple such as a speaker-mic, then Mars' idea is probably better suited for that.