How do I make a combobox accept user input?

Well, the only (be it ultimately insane) i can think of, is to check for the mouses coordinates:
if the mouse is hit over the text writing area, unhide a textfield underneath, to be placed over /in shown place of the combobox until eg:tab or return are hit, otherwise have this text field hidden. too wierd.

This is where i would give up and start making my own scratch gadgets out of canvases, temporary windows and the text command....