Allowing multiple items in column while using select searching

Thsi is kind of a confusing thing to explain so here's an example:

http://live.datatables.net/kixurigu/1/

Basically I have a client that want to tag one row with multiple items. For example they have a row that has "Offices" and for each row they want to be able to add multiple, e.g. "Sydney, Tokyo" but still have separate items in the dropdown search.

Try searching the "Offices" dropdown.

Any help would be appreciated!