Appdeploy is a very good resource for finding out things to specific packaging types of scenarios. A big one being how to preconfigure a package.
Here is a link for somewhat dated material on RealVNC. It will probably get you going in the right direction. It looks like you'll probably need to manually set the password on a test box, and then go into the registry on that test box and extract the appropriate registry value for the password. Then you'll need to add a registry poke for this value in your package.
Read through the Notes section on this web page:
We used a similiar scenario when we moved our manufacturing to another facility. We virtualized the system the group pulled reports on. Rather than trying to educate manufacturing staff, we used VNC to allow easy remote control of the system.
I used AdminStudio to capture before/after snapshots of both the server and client (with password and all connection settings). I built the snapshot into a stand alone MSI and this has worked great.
Obviously, only have had to deploy the server portion once, but have installed the client side about a dozen times.
Let me know if you have any questions about it.