When I put my spoiler on (mine didn't come with a light, so can't help there, but is a Genuine Subaru Accessory part) I needed to drill 2 holes for the studs/bolts that are in the spoiler, which mated up to 2 very dodgy looking plastic "nuts" which pushed into the holes I drilled, which then the studs pushed into.

Im pretty sure the studs are there to hold/secure/centre the spoiler while you pack a sh!tload of glue/silastic/urethane (I used Wurth Windscreen Urethane) to the spoiler which actually secures the spoiler to the car.
I also used a heap of masking tape to hold it dead straight and didn't drive the car over a weekend while it cured.

I wasn't to sure if the urethane would hold, so I did a "test" to make sure it was strong enough.
Test - pull the car along by the spoiler *.
It held, didn't budge, and have done this a few times now when im too lazy to walk around the front of the car to push it backwards.

* Do this at your own risk.

A BH9, but same thing.

No pics.

The kit came with a template, but only for the sides, not the middle, so drilling the holes was abit of guess work.
I dabbed grease onto the studs, pushed onto the tail gate and voila, the studs left marks where to drill.

The nuts aren't actual nuts, just plastic locators.
Drilled the holes, pushed the nuts/locators into the holes (cannot get to the outer skin from inside the car without drilling BIG holes in the inner skin) and pushed the studs into them.

Goodluck!
Pics when you've done it

Ok so i finally fitted it and it looks good.

I managed to line up the two bolts connected to the spoiler and marked the places to fit them using the window washer as a center point.

The measurement was 41.75cm either side of this.

The problem was to find the correct height from the back window...i measured and measured and tried to work it out but in the end the hole was too low by about 1cm.

Once i made it slightly bigger/higher using a file drill bit i fitted it and bolted with the two nut's and spring washer on the inside of the boot lid.

I then made another slightly bigger hole for the brake lights and then worked out where the other bolts should go.

I then used silicone sealant round both sides of every fixing then when it was secure i used more sealent and neatly finished with my little finger round both sides of the attached spoiler.

Left for a day then polished and admired!

The only downside is it's white and my car is silver but i quite like it!!!

Alex