If you want RG, you're best bet is to go for a Mercury (about $110).  It has a lower differential and flare rating, so it won't turn as hard on the back end. Tell the pro shop operator what you want it to do and let him/her watch you bowl a few frames so they can get a better idea of what to do.  If none of that works, polish the ball to a higher grit to get more length.  You may also want to look at a Saturn as well, but since it's a solid reactive, it'll move a little sooner and have more of a arcing back end than the Mercury.