THinking about it more, I'm positive you can do what he/she (sounds a female nickname but that can lie...
) wants, using the control-source of the other fields as a query/SQL based on the "input" bit. If you create a drop-down, and use the wizard doo-daa to make it, you could look at the control-source, and modify it for use with a text-field.
Then you can either have a button to click which runs the append query, or you could probably put it as the "on lost focus" event- though this may cause problems if you selected and de-selected without typing anything- or if there were no matches.