The new Select-CM allows you to do this in mono. In other words, this is a special capacitor selector switch that is designed to work within dual-mono setups, either line-stage or power amplifiers. In addition, this switch differs from the stereo Select-C in that the Select-CM offers four positions: mute, C1, C2, or C1 & C2 in parallel.
Almost all of the GlassWare line stage PCBs hold dual output coupling capacitors, which allows you the ability to chose the sonic overlay that the music being played requires. For example, the coupling capacitor that sound just fabulous with a recording of a lone blues singer playing the harmonica might make recording of a dense orchestral performance sound clouded and blurred. Of course, a different coupling capacitor might invert these outcomes. The Select-CM's last position, where both capacitors are in parallel, is fun, as you can hear the blending of two radically different sounding coupling capacitors, such as PIO in parallel with polypropylene film. The result often sounds much different and better than either alone.