Is there a way to change the location where the Software Update service stores the files ?

Is there a way to change the location where the Software Update service stores files ? I've directed the caching service to an external drive and that works fine. I'm using an older MacBook Pro for the server and it has a small hard drive. I don't want to fill the internal volume up with a ton of files that I don't really need - I just want to get a better idea of how this service works so I can deal with it in places where I might do consulting.

Thanks

B