I use the 1/4" x 1/2" Basswood Strips, Bought at a local craft store. Been a while since I looked for 'em, so don't know if they are out of stock. I had bought a bunch of the Screen Molding and cut a lot of ties, but decided they didn't look right. They match the width of the metal Tie at the bottom, but too wide to match the top, which is what you see above the ballast. So, I went with the 1/4" x 1/2" Cut scrap pieces to fill in the open end of the metal tie.
My first try to see how it looked.
I cut the un-couple magnets out of O-27 Track, and splice them into my O Track
So, That's how I did it.