I don't think you can't controll that without messing with the source code
look at kmixdockwidget.cpp
and there is a line
Code:
MixDevice *masterDevice = (*mixer)[mixer->masterDevice()];
then in mixer.h i see
Code:
/// Returns the number of the master volume device */
int masterDevice() { return m_masterDevice; };
so if you play with that return code you might be able to get what you want
m_masterDevice = 0; is in mixer.cpp
you can see what the mixer device numbers are by looking at ~/.kde/share/config/kmixctrlrc
once you do configure in the top dir of kdemultimedia you can move into kmix directory and do makes and make installs from there