bkrosco...
Easiest way to do this and I have many like this for my customers.
Create a new domain in Plesk and then instead of physical hosting, set it up as a frame forward.
You then go to GoDaddy and repoint the second domain to your nameserver and let Plesk sort it out.
Simple actually. With a frame forward the viewer will be seeing the domain as if they typed that in directly.
Lee