You need to find one of the old style, sheet metal sight brackets. Take the screws out of your cable guard, and mount the bracket between the bow and the cable guard.
I think Cobra still makes one and you can still find them, but they're getting kinda rare. Not much profit in a $10 sight when it's gotten pretty easy to sell fancy hundred dollah sights.

I've even seen 'em at WalMart a few times, but you'd likely have better luck nosing around in the dusty corners of a pro shop that's been around a long time.