Thought I'd share this if others are trying to achieve it for demonstration purposes. The instructions are step-by-step and covered in more detail in the blog post.
With our next workshop planned for tomorrow, we wanted to show the attendees how to send GB Coins from one wallet to another live on the same computer (Windows), so I began experimenting to find a way to do this.
When you try to start a second instance (copy) of the same wallet you get this error: Cannot obtain a lock on data directory
And when you get past the above error, you get another error: Unable to bind (screenshot below).
After some testing we managed to get past both errors and get two working but separate wallets on-screen, with each wallet successfully sending coins to the other one
Source:
http://blog.gbcoinfoundation.org/how-to-run-two-wallets-of-the-same-coin-at-the-same-time-on-the-same-computer/