I built the additions setting VBOX_ONLY_ADDITIONS=1, but I can't test them right now - my today's 8.99.7 panics when I try to start Xorg under VirtualBox, also 'Xorg -configure' crashes. I am not clear how to pack them and install them - I have:
...
bin/additions/vboxvideo_drv_70.so
... (a bunch of similar drivers)
bin/additions/vboxmouse_drv_112.so
bin/additions/vboxguest.kmod
bin/additions/VBoxControl
bin/additions/VBoxService
bin/additions/VBoxClient
lib
lib/additions
lib/additions/RuntimeGuestR0.a
...(more archives)
lib/additions/RuntimeGuestR3Shared.a
lib/HGSMIHostR3Lib.a
lib/VBoxRTImp.so
lib/libXcomposite.so
lib/libXdamage.so
lib/libXfixes.so
lib/libXext.so
...