It would be good to remember that soap is a "wash off" product and that any type of benefit you are seeking from vitamins would be best suited in "leave on " products such as creams and lotions that has a better chance of penetrating the skin layers . It is also good to note that few oils are high in vitamins and minerals as well as anti-oxidants , botanical additives can give an extra boost as well .
ETA: Avocado Carrier Oil contains Vitamins A, B1, B2, D, E, and Beta carotene. It is classified as a monounsaturated oil and is best suited for dry skin conditions in topical applications.
Argan Carrier Oil is rich in vitamin E, carotenes, antioxidants and essential fatty acids, is used for massage, facials and as an ingredient in anti-aging cream.
Black Cumin has a high amount of A, B, and C Vitamins and minerals including potassium, copper, zinc and selenium.
These are just a few oils from my list that shows you that vitamins are already there in the oils and you just got to know the beneficial properties of the oils , and coupling them with the right botanical can boost the desired effects that you seek. [just MHO]