I came across a solution the other day that I hadn't seen yet online, so I thought that I would share.
I was practicing with some rosettes and was running low on BWB laminated purf for binding the edges of my rosettes, so I used some hand plane shavings from a walnut offcut I had.
fantastic!! ive done a similar tehnique in the past , minus the inner and outer walnut ring. i love wooden rosettes. Abalone are pretty but so overrated.
It does allow flex but that gap is just the part that goes under the fingerboard, so no point in making it look nice. My sides over the end block are the same. sometimes I leave up to a 5mm gap as im only going to put a butt strip in there so i don't worry about joining it.