Another possible approach is to drill a 3/4" hole in a piece of scrap wood with the fostner bit. Then clamp the scrap piece on top of the work piece lined up properly then use the hole to guide the fostner bit into the work piece.
If concentricity is a major issue (assuming the work piece is round) mount the work piece onto a lathe then spin the work piece instead of the drill. A dial indicator would allow you to line up the 1/2" hole with axis of the lathe very acurately making the 3/4" perfectly centered over the 1/2" hole.