Hi there, Argan Oil is the magic ticket you are looking for in this case. Just fill it up to 1/4 or 1/2 full, let it hang out for a day or two to absorb some smell molecules, if it's something like mostafa you will have to physically shake the sample to get the two to mix, it might take several days for a solid oil like mostafa before they mix. I have actually refilled the vials halfway twice in the same sample with argan after the sample was almost gone, and was able to get 2-4 extra wears from it. Sometimes I would combine it with something similar in profile if it's 2nd time rinsing it out with argan, since it's faint at that point.
Please note: although Robert likes the idea of mixing argan with his bottles to top them off to avoid oxidation, I don't recommend this route. Even with a normal 3ml bottle I would wait till it's almost gone before mixing a little argan oil to get extra swipes. The reason being is the Argan oil changes the profile of the Oud, it smears the scents out farther apart. For instance, Mostafa will no longer have a huge fecal hit when putting it on after diluting with Argan, it goes right to the citrus notes that would show up a little later on the drydown. This analogy works with almost all other oils, it smears the notes apart and you don't get that rich intense hit of odors you normally would, and you skip the first hour or two of normal scent progression. Argan oil has a slight nutty smell/flavor, like a very mild sesame oil. If you want to try an oil that is less viscous that also never turns rancid like Argan, try Moringa oil from the seeds of the Moringa tree, this oil is colorless and ordorless, but less thick.
I have used argan oil on my face every morning for five years, and it got rid of all my wrinkles, and i use some in my hair and my hair is very thick and shiny. Ensar's Adam even teases me now calling me Guapo. I suggest buying it from bulkapothecary or saveoncitric, and get a gallon it will last you 2-3 years.
I have bought some Ensar oils on ebay that I suspect were cut with Argan Oil ( note: this is not in reference to Oudamberlove who has a great ebay channel with lots of rare goodies if you like), so please be careful out there ok. Cheers.