In stock form, the Arrow does not have two bays for aileron servos. You will have to build a second bay to accomodate the separate servo. This is not difficult, and you can use any of the techniques already mentioned.

I've been through two Arrows. My current Arrow is flying with a single aileron servo, so I can't tell you if flaperons will make any difference (assuming that's why you're interested in the dual aileron setup). On a previous Arrow, after a higher than normal speed encounter with Mother Earth, I re-built it with dual aileron servos mounted outboard in the wing, and also cut the ailerons and created flaps (more servo mounting bays!), then set the whole thing up to perform "crow" mixing. The Arrow climbed when I dropped the flaps, but I never got to really figure out what it would do at lower throttle settings. It was an interesting experiment, unfortunately cut short when the engine failed on a really windy day and the plane paid a visit to our local gravel pit. The wing didn't survive that one!

You can also look at a Midwest Aerostar, one of the other high winged semi-symetrical aerobatic trainers. It's designed for dual aileron servo's, and comes with the servo bays already cut in the wing.