I've had the fleece for it in my stash and earmarked for the lining for just as long as the cowl has been around. This horse pattern seems appropriate given that I named it after a horse I was riding the winter I made it. With really no other excuse other than just "it seems hard to do" I sat myself down to figure it out. In the end I just attached it the same way I would a binding to a quilt, with a ladder-like approach to the whip stitch. I used a sturdier thread rather than just plain sewing machine thread and I think it worked out just fine.
All I had to do was cut the fleece a little larger than I wanted, sew one seam, and then whip stitch on while folding the edge under. The cowl is narrower than the horse pattern repeat, but I lined it up so I had at least a few faces peeking in when I cut the piece out.
The funny thing is that after all was said and done, I actually got the fleece in upside down relative to the way I like to wear the cowl. Oops! Well, only I will know.
And the most important part, it was great to wear! With just a small amount of effort, it has become one of my favorites now. Thumbs up for sticking with it.