I added it /etc/rc (at my own peril). In 5.6, they added they net option to mount so in fstab I label the encrypted file systems as net, then call bioctl before the net partitions are mounted and fsck'ed.
I also called it 3 times: bioctl || bioctl || bioctl to give me 3 shots at the password. ;) Maybe there is a neater way to do it, but it got the job done. Tim.