I would do the bucket drip method to acclimate him. Float the bag as you normally would to fix the temps. After floating, pour the water in the bag into a bucket. (youll have to put something under the bucket to tip it up so that the coral is covered with water.) use a peice of airline tubing with a gang valve or tie a bunch of loose knots in it to get it slowly dripping into the bucket. About 2-4 drips per second with a 5 gallon bucket. When the water volume in the bucket doubles. (you can set the bucket level at this point.) dump out half the water in the bucket and drip more untill the volume doubles again. Take the plastic bag that it came with and scoop him out (water and all of course.) submerge the entire bag and pull the coral out (I dont like to expose critters to the air, dunno if it makes a crap, but I dont do it.) While the bag is still under water, twist it off and pull it out to keep the water out of your tank. Throw it all away.
That is a complicated process, but it is the lest stressful. I can't remember where I read that proceedure, but I like it. and I have yet to loose a fish or coral to acclimation stress since ive started doing it that way.