Good point. It would surely be very annoying to skip through a track when you try to change volume. So how about a little visual indicator which tells you which mode you're in. And a distinct sequence of short beeps to give you the audio feedback (low-beep high-beep to indicate seek mode, high-beep low-beep to indicate volume.) This wouldn't stop the fat-fingering from happening, but at least you'd know which mode you were in to start with.

Or the alternate solution (which I also recommended previously) would be to have the seek mode "time out" after 5 seconds or so... So when you casually reach for the volume knob, you know you're going to get volume, but when you tap the knob then turn it, you'll get seek.