Duncan, the best way I know of plumbing at distance is to set up your rig and shot the float as normal. Set the depth at what you estimate it to be at the range you will be fishing and then carefully squeeze a swan-shot onto the bend of your hook,(avoiding the point). Then cast out, if you are overdepth the float will cock as normal, to get the right depth keep moving the float down the line untill it is just showing, it's fairly accurate. Or if you are fishing hard on the bottom you might want to look at fishing a Polaris float with a running leger rig. Much simpler.
Personally I never clip-up with a waggler, to get my mark I use the reflection of a feature on the opposite bank and cast to that.