Hey Betty, I use Aleen's tacky glue in the brown bottle. It will glue two oiled boards together as long as the oil has dried. Lemon oil never dries. I use a 50/50 mix of boiled linseed oil and mineral spirits. The mineral spirits thins the oil and allows it to dry much faster. Once dry, you can glue things together with the tacky glue. But what I do is glue the backer board to the workpiece first, then soak the whole project at once. Then I us compressed air to remove the oil from between the two pieces and the fret holes.
Aleen's tacky glue is available at craft stores like Michaels or Hobby Lobby.