[eluser]WanWizard[/eluser]
A lot easier is to set up a router in your local network (i.e. local to the internet facing interface of the webserver), add an extra segment, interface or VLAN to that router, and assign that interface a subnet from across the globe.
Connect your PC to that subnet, give it an IP in that range, and start testing. The webserver will see the IP you want to test (it doesn't know that you're not on the internet), the router will route the return traffic back to you test PC because you're locally connected (no route needed).
If you want to test latency, get a linux box and NetEm, which can add latency, packet corruption, reordering and more nasty stuff to your connection.
edit: you could also do this with a linux machine, two interfaces, and a virtual machine, if network stuff scares you...