Run, don't walk, to the nearest hardware or home fixit box store. Go to the paint dept and ask for the cheapest bucket of mis-tinted or returned paint. Latex, oil, whatever. It all works. Buy a cheapy brush 6" wide.
Slap a coat of cheap pinkish-puce-purple-whatever on those backs and you are good to go. It will seal nicely, and the more obnoxious the color, the easier it will be to tell if you have removed it when you take it off with a scraper or sandpaper. When dealing in volume, this is one case where a cheap shortcut won't hurt you. I have picked up gallons as cheap as $8, enough to do about 50 staves, two coats each, including ends.
As far as I know, there is no whitewood that is totally safe to debark without sealing.
