Morning Paul.
Sounds like your in the same boat as me, although I think I may have just located one the right colour for mine.
Like you say, I'm guessing it bolts in through the existing boot lip, which is similar to the bravo but that bolted through the glass.
With this i just pulled the bolts off and tiger sealed it on and its never budged. So depedning on the weight I may just do the same with my Stilo as dont really fancy taking a drill to her.
If and when I get to it matey, I'll make sure I post it up on here for people to see as no one really seems to no about retrofitting a stock spoiler.
All the best.
Lee H