I run a side business sewing bikepacking frame bags and fork mounted bottle/stuff sack bags (the "Everything Bag").
(Posted in classifieds due to commercial interest - moderators, we can move this elsewhere if more appropriate).
For years I've experimented with different ways of mounting cages to forks without the threaded bottle mounts, and have finally found an "off the shelf" solution that's mostly perfect. It will work with my Everything Bags or any other bottle cage, Salsa Anything Cage, or similar.
Here's the write up on my blog.
http://cleavelandmountaineering.blogspot.com/2016/11/new-everything-bag-mount-testing.html