Try mineral spirits
I clamp these pieces in my vise (with a space to prevent racking), clamp or hot-glue a block to the edge the plane will exit on (or just cut the piece extra wide) to prevent blow-out, then dab some mineral spirits or rubbing alcohol to the end grain. This will soften the grain without the damage water would cause, and it will not affect your finish, making the plane glide perfectly along the grain. This method has never let me down. Also, wax the sole of your plane if you are not already.