I either figured it out or found a workaround. Here is what I did:
1. Split the cells
2. Changed the width of one of the check boxes to the same size as the left column
3. Wrapped the check box in a subform
4. Dragged the subform into the left column
5. Selected the subform and the right column cell and merged cells
6. Added the second check box into the subform
7. Changed back the width of the check boxes to what they need to be