Some questions to help us understand your problem: what do you mean by "lighter" oil? do you just have a mixture of oils or are they mixed with other things as well?
In chemistry there are a few standard ways of separating compounds. One is distillation in which compounds can be separated because they have different boiling points. Another is extraction in which compounds are separated because they have different solubilities in different solvents. The problem you are posing here is complicated because "jojoba oil" is not just a single compound https://en.wikipedia.org/wiki/Jojoba_oil - it is a mixture of many individual triglycerides which means it does not have a single boiling point and a range of solubilities. The lighter oil you are referring to might actually have properties in common with some of the "lighter" portions of the jojoba oil making separating all the jojoba oil components from another oil very difficult.