JQuery :: AddClass To Amend An Existing Class Without A Space?

I have been trying out image replacement on radio buttons and check boxes for styling forms. In this case I might have something like:

<label for="usd" class="currency">USD</label>
And using addClass
$(this).addClass('hover');

It turns into

<label for="usd" class="currency hover">USD</label>

The problem is that in IE6 if you were to have two custom radio button classes on the same page then the first one takes on the styling of the last one because IE6 can't figure out the chained class. Ideally I would want the class to be amended on hover toclass="currencyhover" instead so I could write a unique CSS class like .currencyhover instead of .currency.hoverIs there some way to use addClass and not have it add a space between the already existing class and the new one? If not, is there some way to trim it