I suspect a "carrier" of some sort of solvent would be the way to go about it, but I honestly don't know.
Something in the back of my (very leaky) brain is telling me Ivo said something about this, maybe about 5-6 years ago.........
I'v also read that there are ways of getting the insides of decanters polished, which might be a bit costlier and certainly time-consuming, but this is such a beautiful beast I think it would be well worth getting it sorted.
Polishing it would mean you could use it.
Warning! If you do find a solvent and use it, do not, under any circumstances, decide to "burn it off".
I one used methanol to rinse a decanter, then (very stupidly) thought;
"I know, I'll put a flame at the top, to burn off the excess solvent...."
WHOOOOSH.
An enormous flame exploded with an almighty bang. Gave me an awful fright....
and I was very lucky that's all it gave me!