First, the XL dies DO FIT through the cuttlebug. Many people on SCS have posted that they do not fit, but indeed they do! The sandwich that cuttlebug recommends for using thicker dies (like the Big Shot dies) is B plate, die, B plate. This sandwich works perfectly with the Big Shot Bigz dies, but the Bigz XL dies are longer than a single B plate. What I do is this...
As you can see, the Bigz XL die is laying to the right of the cuttlebug. The die is HUGE!!! Believe me... it DOES fit through the cuttlebug.
I place 2 B plates end to end. When they are end to end, they are actually slightly longer than the XL die.
I place 2 B plates underneath the Bigz XL die and 2 B plates on top of the die. I'm embarrassed to show you my one B plate.... lookie how marked up it is! That's the plate I always use when cutting with my Nestabilities! I think it may be time for a new set B plates to replace that awful looking one!
Finally, I run the whole, giant sandwich through my cuttlebug. It fits just fine and does the job! No Big Shot required to use the Bigz XL dies!
The only thing I've noticed with running the XL dies through my bug and using 4 B plates is that where the 2 B plates meet, you will get a slight indentation.. similar to a weak score line on your cardstock. But honestly, I don't think it's noticable at all! Once you get your creation decorated, you don't notice a thing!
I hope this helped answer your questions on how I use the Bigz and Bigz XL dies in my cuttlebug! Have a great day!!! :)