I wouldn't try adding olive oil - if it gets into your water I think it will just cause your skimmer to go crazy.
I also run a line from the skimmer cup into a 5g bucket that I keep under my stand.
I suppose you could try something like a electric float switch, but you will need to get one that doesn't turn back on once the water level goes down. Beyond that, it might not work if it gets coated with gunk from the skimmer cup.