Don't do it!
Like Pappy says.
I had some Oregon Yew billets with a few bug holes in the back. Got to within an inch of finishing it and it exploded.
Snapped clean across the back where a bug hole went in and then turned to run square across the back just beneath the surface
cutting the sapwood almost clean in two.
Fine on the belly if you fill, but fatal on the back, as filling achieves nothing, it will just pull away from the filling material.
Back it is the only safe option.
Del