I'm not clear on what you mean by "inside". I will use a drop-down to make the selection AND have an overlay (merge or regular field) that shows the value (likely related) of the text, instead of like the ID.
This works well. Think in terms of the "show arrow" or show the calendar icon. If you make your selection field offset (left or right) with ways to hide the contents, except when selecting, that also helps the overlay be more prominent.