If you set it up so that no one can actually pay you any money, wouldn't that be sufficient?
If you are really concerned, create a page explaining the concept behind the site and link to it from every page.
You could put the disclaimer on the page people get to if they try and pay.
I'd do some research before using the word imagineering. That's a division of Disney (WDI) and they probably own a trademark. I've worked on the Disney fringe in the past and I know they guard their trademarks rigorously.
If you accept money you need to deliver what the customer is agreeing to buy. Just don't accept money if the products don't exist.
I suspect you need more official advice than is available here.
In the UK my understanding is that if you offer something for sale at a certain price you are obligated to deliver it at that price. That law mainly concerns the price, in that you cannot attract attention with a low price and then charge more, or charge more due to the color or sex of the buyer etc.
It also prohibits offering something and then refusing to sell it or selling the same single item to 2 or more people etc.
So while the law is not necessarily designed for such a thing you could well end up getting tangled in it.
One option is to put "Coming soon!" for each and every item, then as someone mentioned just put your disclaimer on the sales link.
Depending on exactly what is being sold, and how it is "packaged [store.theonion.com]" it can be done.
Make sure you add sufficient disclaimers "this is a parody" or "this is a what if" site and NEVER have a click to pay link and most likely you'll not have any problems. One might look at it the same way as those "popular" magazines about science and mechanics during the 1950s-1990s chatting up new technology that was NOT quite there yet.
That said, you might want to chat with an attorney based with trademark/manufacturing/business expertise.
It is one thing to say "Fabulous Wireless Widgets!" with descriptions opposed to having a what appears to be commercial site offering fabulous wireless widgets.
Best suggestion is a "You've been pranked!" checkout if determined to make it look like an ecommerce site.
Current quantity: out of stock
[Email me when this product is available]
I find the concept amusing and wish you luck.
My concern would be that I would be dreaming up smart ideas and names for products that don't exist, and that other people would then go out and make them (and possibly trademark them).
Getting a cease and desist from "Acme Non-stick Glue" would make life interesting.
I also like the concept, but the Disney warning should be taken seriously. There is considerable debate as to whether imagineer or imagineering belongs to Disney - there are plenty of other usages and context of those terms, and there is the 'generic word' issue. If that word(s) is crucial, you will want a lawyer for sure from the start. Mickey Mouse is a Mafia thug:)) If it is a word that isn't crucial to concept or SERPs, then I would use it and be prepared for the possibility of having to do a search and replace down the road.