This is my first post after joining APUG, and I'm happy it can help someone else.
I have a Widelux F7, and custom-made my own carrier from an Omega 35mm one I picked up cheap on eBay.
I measured out a Widelux neg, carefully marked it out on the carrier, and then took it to my local high school where the metal working teacher was happy to use his plasma torch to cut it out perfectly.
I then filed it smooth, and used heavy sandpaper (for metal) to make it perfect.
The nice part is I get a nice black border when I print full-frame (which I do on all negs).
Hope this helps - it was ridiculously easy.