Okay, I just tried this (and my first refill attempt, at that!) and it seems to work fine. I took what I figured to be an almost empty French Vanilla Ice Cream cart (my current favorite) and figured I'd top it off. By way of experimentation, I took 15 drops of Smilin Special Menthol and plunged it. Then I did the world famous Taryn Spin and found I could put another 8 drops in. Spin again, and wipe it off. Looking in the hole I could see some liquid, so I gently blew it out into a napkin and wiped everything off again. Since I'm incredibly impatient, I immediately tried it out. No juice in the mouth, although there was a bit of a gurgling sound that might indicate it needs to absorb more.
And wow. Let me tell you something: FVIC + Smilin Special = EPIC WIN.
SOOOO good, and is now my new favorite. I'm going to try and exercise some self control and let the cart sit overnight (I've heard that's recommended), but this seems to be a winner for a quickie refill, and let me just say again: Do youself a favor and try mixing Smilin Special with FVIC. It's absolutely heavenly!