Depends on how bad you've got the dreaded DIY disease

. With a good tablesaw and enough time I think the Backebo door could be cut down. The joinery on Backebo is really cool, and CAN be replicated with the right tools.
There's a fast way and a MUCH trickier way to cut down a Backebo door.
Fast Way:
1. First you'd have to figure out how wide the door would need to be.
2. Then cut the door lengthwise somewhere near the middle.
3. You should now have two sections of the floating panel for the middle of the door, rip one of them to the correct width (cutting off the section from the middle NOT the side that has the machined/decorative thinner edge) so that when the two sections are rejoined they are the right width, allowing for the amount that the panel should extend (use top and bottom grooves to determine required overlap) into the grooves on the stiles.
4. Glue the panel back together preferably using Bessey K-Body clamps or equivalent. If done well you shouldn't be able to tell the panel has been modified at all, as it already HAS joints in it just like the one you just made.
5. Cut down the rails on one side so that when the ends of the rails are rejoined they will be the right length for the new door size, if you make sure to cut it on a different side than you cut the panel the cut lines will not line up and will tend to disapear when viewed from a distance .
6. Rejoin the two cut rails using your prefered method, though unfortunately Backebo rails are *just* too narrow to use a Porter Cable Face Frame biscuit, so that's out. I'd probably use a spline of a contrasting colored wood (walnut?) to make a feature of the modification, or a scarf joint for greater strength.
When you're done you should have a very fine joint line running through the rails from top to bottom, but I imagine it would look fine, and probably a lot better than a cover panel as it would be an exact match for the rest of the doors.
Tricky way:
If you don't want the joint in the middle, it IS possible to create the joint on the end of the Backebo rails using a tablesaw and a good router/shaper table, though it would certainly be a bit tricky. It'd take a while to write up the sequence for that, so I'll just say I'm pretty sure I could do it. If you decide you'd like to go that route, I'd be glad to chat about how you might approach it.
If you DON'T have DIY disease to quite that extent; first, congratulations! Second I would suggest taking the door to a good cabinet shop and see what they say, they can probably cut it down for you, though I'm sure it won't be cheap. You're only talking two doors though?
James