YES! You can absolutely refill ESSIO pods with your own oil, when the pods are empty. In order to do so, you need a 3 ml disposable pipette, which you can buy from Amazon.com ($1.50 for 20 pipettes). Simply remove the cap from the pod and dispense the oil from the pipette into the pod. Replace the cap. ENJOY!
Note: You can do this only with pure essential oils. If your oil contains a carrier oil, it will most likely not work, because the high viscosity of most carrier oils, will cause the oil to flow through the filter at a very slow rate.