Hi, Valletta. No, don't premix powdered Vitamin E with oil. Tons of information is covered in the ECHorsekeeping link Nancy provided, including a warning against premixing.
Vit E Recommendations.doc

There's also a price comparison of the various forms of Vitamin E, tho with recent price jumps it probably understates the costs. 
https://ecir.groups.io/g/Horsekeeping/files/-Vitamin%20E%20Compare%20Cost.pdf 
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