Fats and fatty acids can be brominated, in fact, brominated vegetable oil is still used in soft drinks in the United States. It's in "FANTA", an orange flavored drink that tastes pretty good.
The problem is, even if you brominate the thing and then do an elimination taking care to make sure all of your product is "cis" and not "trans", you're still not going to get the unsaturation in the right spot!! the location of the unsaturation(s) is critically important in the health effects of fatty acids, so unless you are trying to make something for its properties as a material (like a polymer or something) this isn't of much use either.
If you really want to do this right for biological purposes, you're probably going to need to construct a bioreactor of some type and get some little critters to do all the hard work for you.