Under these conditions you can not depart VFR.
That is pretty clear from the regulations.
You can only fly in IFR outside CAS but there is no reason why you should not ask for a service from a nearby unit as soon as you find yourself in IMC.
If there is no unit around that can give you a service and you feel uncomfortable you would probably benefit from a revision of your decision making processes before your next flight as it means that you have taken off in rather cruddy weather from an airfield without an IAP.
Some would say that is not the cleverest thing to do if you are in a twin, most would say it was unclever in a single.
FD