This is a sample project to show how you can implement sticky headers using the UX-expression y(element) introduced in 0.35. If you have a better solution, please post a link to a repos here and explain what improvements you have made. If you want to refine this example, just fork it and send a pull request.
Nice timing, we published an example on how to do this exact thing yesterday 
https://www.fusetools.com/examples/sticky-headers
I noticed a minute ago… I am on vacation in Bali, so took a week until I got around to post my example code.