If your low-porosity strands are becoming super oily with a pre-shampoo, it's important to assess how often you are using this step in your routine. Some low-porosity hair types needn't use a pre-shampoo with each wash as these types generally soak up less water than others. When you do choose to incorporate a pre-shampoo, you can use a lighter oil such as Squalane or grapeseed oil (keep in mind a little goes a very long way) as these are much easier to wash out. If you'd rather avoid oils entirely, then you can opt for a humectant such as aloe vera to use instead. If you happen to find that your hair is low-porosity toward the roots and high-porosity toward the ends then you can choose to only apply your pre-shampoo to the areas that are high-porosity.