Yes, you can slide nails or wire into the slide grooves
The 'official' hanger should
be 2 'C' shaped hangers that wrap around the light from the top and slide in the same groves.
EDIT: just now thought of this, but long stiff wire (stainless?) through the slide grooves would allow a Finnex light to go on a slightly longer tank than the light, a la Mainland's fixtures.