Populating a drop-down based on checkboxes

Hey folks,

I am attempting to provide users a drop-down of values based only on boxes they have checked.

The user has the ability to check up to 4 boxes (Zones 1-4) and I am attempting to provide a list in a drop-down format on 50 cells that will only allow them to select a value from the boxes they have checked.

For example:
If the user selects Zone 1, Zone 2 and Zone 4, they should only have the ability to select 1, 2, or 4 from the drop-down list.


My initial thought was using data validation, a named range and passing an array based on the checkboxes but I am not sure if I can add and remove values from an array in this manner.

Any thoughts? Is this even possible?