Yeah, with my second post there I was just kidding. If you remove the clutch spring bolts and pull out the clutch springs, you should be able to take a caliper to it and measure them. There should be a tolerance measurement in the service manual somewhere I'm guessing and you'll be able to tell if your springs are out of spec. If your clutch springs are too compressed that would cause there to not be enough return force. Just a guess though.
If you aren't getting any joy messing with adjusting the cable or doing things like that, it sounds like you need to knock the cover off and actually take a look at the clutch itself.