How do I set a custom upload directory for each sub site on my metwork

Hello,

Is there a way to set a custom upload directory for each site in my multi site network? I would like to have any files uploaded into http://mymainsite.com/media and to http://mysubsite.mymainsite.com/media for any sub site. Also, for any mapped domains, I would like files uploaded to http://www.mysubsite.com/media. Is there a way to do this?

Additionally, is there a way to put image files in a sub-folder of media, i.e. /media/images? And PDF's into /media/pdfs/?

Please let me know. Thanks,

Michael