Maybe you can use 2 different directory scanned by s6-svscan(one s6-svscan command by directory). One for your boot process and the second for your X session. Then init your compiled database by s6-rc-init when your second directory is ready and bring up your service with s6-rc. Now you can make what you want "on X session" without touching your boot process. Not sure that a good solution but i use it as it on my system and i have no issue.
-- Eric Vidal <e...@obarun.org>