I know how they feel. I have to do this for my software all the time.
Most of my products are "wizards" that generate code for advanced functions that my customers can then add into their websites.
Even though the generation process for most of them actually is very complex it's still nothing that the server can't perform in 10 ms. But people don't like that. So I always put in a spinning progress bar for 5-10 seconds and then they're happy.