If you have the capability of getting onto the Internet from a different machine, Dial-up, direct connection, etc.
You could always consider manually updating the SEPM server on a daily basis.
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2008030710560348
This will allow you to download the necessary files for AV/AS etc. at your convenience and place them into the server whenever you are ready to do so. It would save you the time of configuring a LUA server, the cost of the machine, etc. As well as the leg work of; plugging it to the internet, downloading definitions, disconnecting from the Internet, connecting to the network, updating server, and than distributing the definitions.
You could possibly do this from home or any Internet connection.
Just my 2 cents.