How do I turn on the check box for year/month folder

In my WPMU install there is no check box for “Organize my uploads into month- and year-based folders” so by default these folders are being created. Working with Marketpress I need to (1) have people upload their images to site/7/ for example then (2) add the link to the csv file. With WP creating month/year directories it is really impossible to tell people where to locate the images. Is there a way to have WPMU not create the month/year directories and just have the images in the upload/site/7/ directory?

Thanks, Dan