im not sure just you can to first loginout game center and AppStore then open game when say you login GameCenter donot login then don't touch any load game , then goto buy gems then login your another ID buy it .
Thank you! I'm going to try it. ;)
if your iphone jailbreaken and installed pirate your cannot buy , try reset all setting not erase when finished reset network setting , when you tuched buy gems you see some message about server error or internet connection problem ?