OS X Lion Connection to Business network?
I don't see a reason not to set up a VPN. You can add the VPN menu to the status bar and your client can simply select their VPN and enter a password when prompted. It's no more difficult than say, a TeamViewer connection setup. (In fact, VPN is arguably easier, since the system stores your username and merely prompts for a password. TeamVewer requires an ID and a password.)

I just began using VPN this week, and it's super easy. Really. To add VPN to the status bar:



Then, your client can simply click to connect, like so:



(VPN info blurred for security reasons.)