Even though I use VirtualBox frequently to run TC, I never wanted to install VBox-OSE-additions.tcz just to be able to use vboxfs. This is due to the amount of dependencies (incl. Xorg) for which I typically have no need or use.
I therefore had a bit a poke around and found the following minimalistic way just to use the VirtualBox shared folders feature:
(1) Install the VBox-OSE-additions-modules-... extension (containing just the kernel modules), e.g.
tce-load -wi VBox-OSE-additions-modules-$(uname -r)
(2) Extract /usr/local/sbin/mount.vboxsf from VBox-OSE-additions.tcz. This file will have to be copied to /usr/local/sbin with the suitable ownership (i.e. root:root) and permission (i.e. 755)
(3) Ensure that the 'vboxvfs' module (for TC 2.x) or 'vboxsf' module (for TC 3.x) is loaded, e.g.
for TC 2.x: lsmod | grep -q vboxvfs || sudo modprobe vboxvfs
for TC 3.x: lsmod | grep -q vboxsf || sudo modprobe vboxsf
After this you can mount VirtualBox shared folders with a command like
sudo mount -t vboxsf -o nodev d-drive-rw /mnt/d-drive-rw
or
sudo mount.vboxsf d-drive-ro /mnt/d-drive-ro
Please note that these steps do not use the additional user (i.e. vboxadd) and group (i.e. daemon) that the VBox-OSE-additions extension creates. But according to my (limited) testing this does not appear to be a requirement.
I guess this could be put into an additional extension. Or the current extension could be split into a vboxsf and a video driver related extension. But I don't consider this to be my call. I was just curious to find a different way and thought I share the information here so that others might benefit from it.
EDIT: Made corrections for the fact that according to the changelog for VBox v3.1.8 "... renamed the guest kernel module from vboxvfs to vboxsf ...". Therefore for TC 2.x (where the additions were based on VBox v3.0.12) the module name is 'vboxvfs' whilst for TC 3.x it is now 'vboxsf'. Plus another minor adjustment to avoid a "hard-coded" kernel version.