To go to cd-writing mode:
rmmod ide-cd
rmmod cdrom
insmod scsi-mod
insmod sg
insmod ide-scsi
insmod sr_mod
insmod cdrom

Optionally, to compress data in the data directory:
cd <directory>
gzip -r *
cd ..

To make the filesystem with the data:
mkisofs -r -J -o <tmpfile> -data <directory>

Optionally, to blank a CD-RW:
cdrecord -v speed=2 dev=0,1,0 blank=fast

To write the filesystem to the disc:
cdrecord -v speed=2 dev=0,1,0 -data <tmpfile>

To go back to regular cd mode:
rmmod cdrom
rmmod sr_mod
rmmod ide-scsi
rmmod sg
rmmod scsi_mod
insmod cdrom
insmod ide-cd