Changing 'search' Part Of Url On Submit

In the process of putting a form together, I'm using a lot of
placeholder variables that I really don't care about in the submitted
action. I'd therefore
like to get rid of them by doing something like:

function my_function
{
document.form.action="/my/action";
document.form.search="?important=1&variables=1&only=1"
document.form.submit();
}

This doesn't seem to work, nor does making an '.action' with an
embedded search string (document.form.action =
"/my/action?my=1&variables=1") Javascript seems to merrily ignore
these statements and simply evaluate the submit call with the html
variables.

How do you modify this value?