I'm thinking in terms of bikes where if your fork collapses, you get injured, which is all bikes.
I got a short education about 'bents, but I'm still pretty sure you would be better off with an adjustable dropout. I probably would decide where the middle of my design range was, and put the fork blade itself near there. The blade would bisect a bar-shaped dropout that would accept an insert with disk brake mounts machined into it. This dropout could be 6" long. If you slotted the blade, the slots wouldn't have to be continuous. Rake isn't all that sensitive as long as you are close. Triangulate the front and back of the dropout to the fork blade with 1/2" tubing. I think it would work pretty well and be a lot safer than trying to clamp at the crown
I have considered building a fork like this for an upright. A little overbuilt, but I don't see that as an issue.