Selenium (Python): How to insert value on a hidden input?

Selenium (Python): How to insert value on a hidden input?

I'm using Selenium's WebDriver and coding in Python.
There's a hidden input field in which I'm trying to insert a specific date
value. The field originally produces a calendar, from which a user can
select an appropriate date, but that seems like a more complicated
endeavour to emulate than inserting the appropriate date value directly.
The page's source code looks like this:
<div class="dijitReset dijitInputField">
<input id="form_date_DateTextBox_0" class="dijitReset" type="text"
autocomplete="off" dojoattachpoint="textbox,focusNode" tabindex="0"
aria-required="true"/>
<input type="hidden" value="2013-11-26" sliceindex="0"/>
where value="2013-11-26" is the field I'm trying to inject a value (it's
originally empty, ie: value="".
I understand that WebDriver is not able to insert a value into a hidden
input, because regular users would not be able to do that in a browser,
but a workaround is to use Javascript. Unfortunately that's a language I'm
not familiar with. Would anyone know what would work?