Not to buck the pack, but if you're going to make an ELB, you'll need some of that sapwood. Mulberry works good in an ELB style by leaving a couple rings of sapwood on the back, and after it ages a bit it's hard to tell that it's not yew just by looking at it. You definitely want to seal the back, though. I would split it and seal the ends, then debark and seal the back. Get one roughed out to near bow-size so it can be drying faster than it would if you leave it in a whole stave form.