Pre-erase JFFS blocks

Hi! Usually OpenWRT erases the free blocks of the overlay filesystem at first boot (that looks like the log I pasted below). I wonder if there is a way to already include these blocks pre-erased into the FW image, so that there is less work to be done at the first boot and so that we can reduce possibilities of mistakes in the production process.

[   60.439549] jffs2_scan_eraseblock(): End of filesystem marker found at 0x0
[   60.485825] jffs2_build_filesystem(): unlocking the mtd device... 
[   60.485887] done.
[   60.501967] jffs2_build_filesystem(): erasing all blocks after the end marker... 
[   69.570530] IPv6: ADDRCONF(NETDEV_UP): wlan0: link is not ready
[   88.315129] done.
[   88.319037] jffs2: notice: (1340) jffs2_build_xattr_subsystem: complete building xattr subsystem, 0 of xdatum (0 unchecked, 0 orphan) and 0 of xref (0 dead, 0 orphan) found.