'Dynamic' adding in lookup-wizard's-table

Hello,
I'm wondering if there's a possibilty to let the user add data to the table the lookup-wizard uses while entering data in the addform like dadabik (a server-side php-script that resembles phprunner in some ways- am I allowed to mention it here <img src='https://asprunner.com/forums/file.php?topicimage=1&fieldname=question&id=2452&image=1&table=forumtopics' class='bbc_emoticon' alt=':unsure:' /> ) does. For example:
There is a field "week-day". The lookup table offers only "Monday", "Tuesday". Now the user should be able to select "other" and write "Wednesday" into a textfield. The next time someone starts the add-form the list consists of Monday, Tuesday, Wednesday....
Perhaps it's already implemented and i couldn't find it.
Thanks!