This is what Kogarah Council is proposing.
The Trans Fats are not a new type of synthetic cooking oil, they are a byproduct of treating otherwise "Difficult to find a commercial use" oils for commercial uses. The "Trans' is actually short for Transesterified, that is, the exact same process we use to make Biodiesel. By treating various vegetable oils by hydrogenation, they can be used in Margarines and Cooking Oils. While the treated fats are now more useful at room temps, it is an unfortunate issue that the transesterified fats are harmful to the human body, with studies linking them to increased Cholesterol levels and increased Heart Disease. It is this same process of hydrogenation that BP are using for their Biodiesel production.
If you can find cooking oil with high levels of Trans Fats, some of your BD conversion is already done for you, but expect a poorer yeild per litre, as the base stock oil is harder to "Crack".