Save your wallpaper and/or ringtone to the device memory instead of the media card. This will allow the wallpaper and ringtone to still function properly when your Tour is plugged into your computer with Mass Storage Support enabled.
Here's a free file manager app that you can use to move media files from your media card to the device memory, and works on the Tour (I'm using it). Scroll down the page to BilbyFile Lite for the computer and OTA downloads.