A html control of type "file" is displayed differently by every browser. So the way to go (I think) would be to add the file control and hide it. Then you could add a text box and a button and try to accomplish the same. Here is a jsfiddle that does just that!
http://jsfiddle.net/CcGrT/
But just curious, why do you want to do this? This just makes your life tougher, since you wouldn't know if anything entered is valid. So I would also disable the text box, leaving the button alone to be in the enabled state!
Hope this helps! If this is not what you're looking for pls. update your question!