Yes it is possible. A script trigger such as OnObjectSave can perform a script that adds the value to a new record in a related table. It can also remove such a record if they select the value a second time, IF that is an option you want to have.
But synching back to the main database can be an issue. You may want to investigate the third party synch tools offered by SeedCode and 360works as a way to get this to work for you.
Ok... so now it looks like we have to learn about scripts and triggers! This could be a long week!
Any useful links would be helpful.