Thanks to John Bauer for sending in this tip:
In the Options menu under the Files tab, several items allow only one entry. The Drawing Template File Location, Printer Configuration Search Path, and Plot Style Table Search Path are a few examples. However, there are times when you need to have AutoCAD look in more than one location for some of these items. There is a way around this limitation. Even though these items allow only one path, they do search subdirectories. They also search shortcuts located in the specified directory. So all you have to do is place shortcuts to whatever additional directories you want searched, and the items in those directories will be found.