You can do this at home on your own. You'll need a set of needle-nose pliers, and you can re-use the hog rings from the cloth seat covers. Make it a weekend project, to make sure you have enough time if its your daily driver. You're going to have to remove the front seats.
Here's a write-up from 40collective.com, the definitive 4.0 mustang site. I recommened y'all sign up over there as well, they're a great group of people and have some incredible 4.0's.
Sorry to the mods in advance if i'm not supposed to be advertising other forums on here... I hang my head in shame.
Black 2005 Mustang v6, 5 speed, IUP, EUP and Leather.
Razzi 1/4 window scoops, Mustang GT Sway Bars, Flowmaster American Thunder Single Exhaust, Clear Front Turn Signal Lenses, Demolet CAI, X-cal2 91 tune, Hurst Comp/Plus Shifter, FRPP T-Lock, Ford 3.73 gears