I just tried this. A Mcdonald's straw was too wide in diameter to fit into the cart, so I cut it lengthwise and cut a piece out. It ended up sort of coiling in on itself. I cut it to be a few mm below the top of the cart. I got about 15 drops in, until it was just over the top of the straw.
For a plug I used a piece of a greenie scrubbing pad. I pressed the end of the cart onto the pad and it held the outline to follow. I snipped a piece off just a tiny bit larger, so it seals the top well. Then I squeezed the filler into the cart above the straw. I pressed it in to sop up the fluid just above the straw line.
So far, it's not flooding, no liquid in the mouth and it's
vaping really well. No funny taste from the greenie material, either.
If I can find a straw size that is larger in diameter than a coffee straw, but smaller than a Micky D's straw, it would be even easier!