I could be wrong, but I don't believe those legs are compatible with the mini. The larger Coralife fixtures have a metal track/groove on the front and back that is used for the attachment of the legs. I don't think the mini has that track.
you could use two pieces of eggcrate or acrylic strips on each side of the tank (about 1 - 2" wide, running front to back) and suspend the fixture between them. you can get away with one strip, but the light won't be centered over the tank.
i've used 3/16" thick (1" wide) acrylic to suspend a 10 gal strip light over a 20 gal long tank. i use eggcrate for heavier fixtures. if you use eggcrate, make sure you place it with the thinner grid wall side facing the water surface. (there are two sides to eggcrate, look closely and compare the thickness of the grid walls on each side. it is thinner on one side. light shining through the thicker side will tend to be focused downward, while light shining through the thinner side will tend to be diffused outward.
You have slots on your coralife mini? I don't. Maybe new ones do? Also, the coralife mounting legs do not work on most coralife minis, unless like chaznsc, had some slots. I wonder which ones will work though.
check a home-improvement store, in the lighting section, it's used as a diffuser for fluorescent lights, of all things
btw, i think i would use the plexiglass (not acrylic as i posted before) strips. it would look cleaner on your 2.5. also, the eggcrate only comes in 2x4' sheets and unless you have other uses for it, the plexi will be far, far cheaper.
I went to Home Depot, bought four L brackets... 2 inch ones I think. I took wood screws and a few washers and attached the L brackets to the light. I removed the little screws that hold the light together and screwed the wood screws into them. I'd take pics, but I'm at the hospital right now. It isn't the prettiest thing, but it cost only a few bucks and works well. I hope you understood what I did.