If you have something long enough to get past the clear goop that keeps the ink from drying out, you don't even have to get the nib off. You can use needles(hypodermic) or a long tipped squeeze bottle https://www.amazon.com/Plastic-Dispenser-Solvent-Applicator-Dropper/dp/B00U7T16CA
They already (technically) are. If you have a bottle of ink, you can get a squeeze bottle with a longer "needle" portion, stick that past whatever is there to keep the ink dry(usually that clear goopy stuff at the top of the ink tube) and you're off to the races.
A lot of people use hypodermic needles.... But I'm scared of someone thinking I'm shooting up heroin
One of these was my first fp, you can also take off the back bit, and get in there with a long tipped Applicator bottle