My opinion would be to trim it. If it's tight and you do need the sliders, you might end up cracking the fairing anyway, in which case you'd still need to replace 'em. Trim it a little and you'll have the clearance needed so the fairing can flex a little. And if the Slider shifts on impact (no speed or low speed even) it won't put pressure on the fairing.
Trim it up. If you can just fit the base of the slider on, you would have a nice guide to trim by. Go by the outer edge of the slider base with a dremel or something. That's what I did when I got mine (for my '04 R6).