Having installed these, as root you can issue the following commands to mount the host filesystem to a guest filesystem.
- guest> mkdir /home/transfer ## this creates the guest directory to which you are going to map the host filesystem
- guest> mount -t vboxsf transfer /home/transfer ## this is normally done as root
transfer /home/transfer vboxsf defaults 0 0
On reboot this generates an error, saying device not found, but still mounts the filesystem from the host. At this point, I suspect it's due to the order in the boot when it tries to mount it being before the VBox additions are enabled. Still investigating cleaner solution.