is there a safe way to fit a tall quill stem (nitto technomic) to a threadless fork?

The problem you have is tensioning the headset before installing the fork.

I am building a bike for a disabled guy and I needed a very high rise stem. I’ve gone for an adjustable one – BBB HighFix – but they do creak a bit sometimes.
Have a look at Humpert stuff – they do loads of stem of all types including ahead ones – maybe something like this on top of a long steerer – http://practicalcycles.com/products/242534–humpert-high-charisma-ahead-stem-1-18-inch.aspx

I’m not sure that there is such a thing (this statement now guarantees that there is a safe solution 🙂 )

You can go the other way and convert quill to threadless, but that isn’t what you want

If the stem and steerer are the same diameter, it’s theoretically possible but not advisable.

If the stem is 1″ and the forks 1 1/8″ then it’s possible but still quite a bit of work involved, and it won’t be very pretty.

You get adjustable headset spacerswhich negate tbe need for a sfa or top cap.

One ofthose would allow you to use a quilstem provided the inner diameter is correct?