If you can get to the 80 yard mark undetected, flash the decoy at the herd buck. Sometimes, if you approach behind the decoy, into the wind, in a kind of semi-circle, it can set him off, and he'll charge inside 40 yards. They will usually charge toward your downwind side.
I have heard accounts of herd bucks actually coming in and butting the decoy, but I have never personally seen it.
Most of the hunters I know that kill a lot of antelope from ground blinds do not use a decoy. Or, if they do, it is a doe decoy.
Best of Luck,