You can set up a portal where each value shown is a record in a portal. The "checkbox" is really a button that performs a script. The script checks for the related record and, if it exists, deletes the related record. If it doesn't it creates--producing your check box functionality. Conditional formatting can be used to make layout text such as a "tick mark" or the letter "x" disappear when there isn't a related record to provide the visual appearance of a check box. (Put a rectangle object in the background for the "box".)
And in FileMaker 13, we now have a new way to hide objects that could also be used instead of conditional formatting.