I basically copied the code for the key and adapted it bit to do the headers.
Working fine on my gentoo box.
Looking something like this then in default/grub
GRUB_CMDLINE_LINUX="crypt_roots=/dev/disk/by-id/ata-Samsung_SSD_850_EVO_250GB_S2R6NX0J363411N-part1 root_header=/luks-header root_headerdev=UUID=cadca53c-3a05-4ed2-84fe-f2d1d03e812e root_trim=yes dolvm quiet spalsh"
If used it will need more testing as I only have my one box where I'm running it.
Feel free to use or discard as you feel.
If you have, feedback would be appreciated
I basically copied the code for the key and adapted it bit to do the headers. Working fine on my gentoo box. Looking something like this then in default/grub GRUB_CMDLINE_LINUX="crypt_roots=/dev/disk/by-id/ata-Samsung_SSD_850_EVO_250GB_S2R6NX0J363411N-part1 root_header=/luks-header root_headerdev=UUID=cadca53c-3a05-4ed2-84fe-f2d1d03e812e root_trim=yes dolvm quiet spalsh"
If used it will need more testing as I only have my one box where I'm running it.
Feel free to use or discard as you feel. If you have, feedback would be appreciated