All skimmers are gravity based. So whatever the highest point of the outflow plumbing will equal the lowest point of water level inside the skimmer.
So, if you plumb the outflow of the skimmer to go up and above the sump, then the skimmer's water level would just as high and may cause the skimmer to overflow. The only way around this is to place the skimmer above the sump or drill the sump.
If you drill the sump, you will still need to raise the skimmer so the water level of the sump is below the skimmer's outflow. Otherwise, the skimmer will again match the water level of the sump and overflow.
Regards,
Carlos Chacon
CoralVue