Exclusivity and licensing for Flash projects

Not sure where to post this, so…
I have prospective client (a local sign company) that wishes to retain “exclusivity” for a Flash project they want me to create for them.
ie: they don’t want other local sign companies to be able to hire me to produce a similar project for them. Ever.

In a nutshell, the project is an interactive online sign design utility for a sign company website.
It is essentially a Flash analog of a desktop page layout application, that would allow the user to easily select the font, color, size, position, etc… for a set of basic templates, calculate the cost, and submit the result to a shopping cart for payment and production.
The entire process is fairly generic, and I fail see how this could be legally construed as protected intellectual property by my client.

[INDENT]The quandary:
I’m not sure I understand how something like this could be made “exclusive” to a single client, or even a legal basis from which to defend such a thing.
I guess I see it as being akin to an online mortgage calculator; you can pay someone to write the code and create the graphics for the widget, but you cannot expect that no one else will ever have one like it.

In fact, I find it easier to see it in exactly the opposite way: they would have to agree not distribute the source for the Flash project to other local sign companies (or Flash developers), or use it as part of a sign company franchising model, etc…[/INDENT]

Does anyone have any experience or opinion in this matter?
Should I endeavor to protect my work with a formal licensing agreement?
Should I just pass on the project?