You don't need to worry about damaging paint with tape; I've still got tape residue from the Gorilla tape I used to attach a temporary tail last fall, but it will come right off with Goo Gone.
If you look at LSR Civics, they all have some sort of decklid extension with fences.
These are built to be low-drag first, not low-lift, so they're generally a pretty good example to follow.