I'd buy the door with the cabinet, rip 'em both and glue the finished door edge back on. If you can't change your layout to eat up the 5 1/2", go for it.

I agree, 4" could be great for those awkward large flat things.

We had that little space, see pic. KD ordered a pullout dish towel holder but it didn't fit. Clever site supervisor cut me 3 little shelves (not shown) and it has become an amazingly useful nook for rolling pins, mandoline, long rolls of foil, etc. much more useful than a towel holder. We had a custom door front to go on it, so all he had to do was hinge it rather than drill it for the pullout, but they do make long baskets that hold like a load of Italian bread that we could have used. Getting the shelves in was hard, though, after the fact.

I left my 5" space open with one shelf - store cutting boards on both levels. You can do something similar with or without a door, or get a rev a shelf pullout insert for between the cabinets.

I put a 3" RAS pullout next to my dishwasher. The only problem is the dishwasher gets what is in the shelf warm when it runs

Practigal just pointed me to this discussion that might help you figure out whether/how to make use of that narrow space:
Pullout cabinet discussion

I currently have a 5.5" base cabinet, with no shelves, where I store platters and cutting boards. Initially I thought it was a silly size, but I've come to appreciate it and might even do two of them in my new kitchen. Good luck with your "hack"!

Thanks everyone! Wow @xochitl, I did not realize you could do something with as little as 3". That is a good point about the dishwasher and making things warm.

Good luck!!

Very nice! I think you'll like this solution.

I can finally report on how we finished this cabinet and created the door.

I needed to use this stubby screwdriver to screw in the hinges. It barely fit.

I decided to create a shelf with the leftover piece of the bottom panel that I had chopped down when creating the cabinet. It was too long, but cutting off the part where the back panel fits in, made it just about perfect.

There was a little bit of chipping from cutting it down (on the left side), but it isn't really that obvious unless you are looking I will probably touch this up with paint at some point.

We cut the door to size, from a finished cover panel/filler we had ordered from Scherr's. I assume you could do this with an Ikea cover panel as well. We had a scrap that was long enough for the door and was finished on the top and the right side of the door. The bottom of and left side was cut mdf, so we covered that with some Veneer tape I got at Lowe's.

It was not a perfect fit, and if you look super close (below) you can see the edge, but it is not at all something you see when you are looking at the door. Mostly that edge is hidden on the hinge side and by the neighboring door.

To drill the main hinge holes we used this bit on a drill press. You could use a regular drill for this, but it will be a little bit harder to keep straight.

After that the hinges are installed as normal and a handle was added.

I'm using it to store pizza making tools. It was definitely worth the effort to create this. I wish the door could match the other doors and drawers with the Shaker stiles and rails, but this gap was just going to be a big filler piece anyway. This probably looks better than that would have, and now the space is useful.

Lisa Great hack! We are tweaking our Ikea design now and didn't even think about creating cubbies. I've spent a good part of today trying to deal with a blind corner without using the Ikea corner upper.

This is a great hack. I might be using it to fill two 7" gaps on either side of my stove! Thanks for sharing.

OMG thank you so much for sharing this tutorial! You have NO idea!