Well you got me thinking again Race and that can be dangerous.
Right to overcome the problem you highlighted. Try using a long shank hook as your top keeper hook. There will be enough shank sticking out for the split ring to be used.
Now as a Pillie is going to hang down below the sinker, before casting,(As they are pretty long skinny things) but in flight will or should sit back and up on the line. As I don't have any pillies to test with don't quite know.
But I see you have had problems with pillies wrapping around the mainline and in flight seperation from whatever clip you use.
Try adding a Relay Clip to your trace. These are adjustable lengthwise. Slide split ring on to the Imp, bring bottom hook up and clip whatever amount of hook you have hanging out of your pillie onto the relay clip.
Your Pillie is now aerodynamic and wont fly around. Impact with the sea will ensure the trace floats free.