I converted my 10-22mm to be able to be used on FF over the weekend. I wouldn’t call it a full conversion as it’s NOT and EF lens, and you CAN damage your FF camera (and possibly 1.3) if you’re not careful, so proceed at your own risk… But, taking canon’s rear baffle out and adding one that will mount on any canon camera is VERY easy. Watch the video above and you can see it takes about ~30 seconds from start to finish. From there you just have to be careful not to shoot at wider than 12mm as the rear element can touch the mirror if you do so.
To get the part needed, call canon’s parts department at 1-866-481-2569. The part number is CY1-2759-000, but I didn’t know it when I called, I just asked for the 28-70mm rear baffle and it was the right part. It cost $11.xx including shipping and I got it the very next day (NJ to RI ground UPS is always this quick).