dynamic upload buttons

Hi,

I'm trying to put dynamic multiple upload buttons in Tapestry with an
AjaxFormLoop component.

But in the "onAdd" event where you have to create a new UploadedFile Object
and return it, it doesn't seems to have any method to do that, because
UploadedFile can't be instantiated by a new.
Is there a way to instantiate dynamically, in the java class of my .tml, a
new UploadedFile ?

Or is there another way to achieve what I want ?