A guy rebuilt a lian-Li case and had that filled up with non-conductive fluid.....
However....there would still need to be something to cool the liquid down...it's not just going to dissipate heat magically on it's own.....create that liquid and you can consider yourself a rich man.
You would still need a streaming jet of liquid bombarding the CPU, assuming that this liquid is kept amazingly cold, generally through an intercooler or something similar and it's a pretty powerful jet of the liquid being onto the CPU core....otherwise you'd still need some sort of block to dissipate the heat immediately.
So no....sorry it really isn't anywhere near 'the best cooling' ever and it'd be a pain in the ass to deal with a case filled with liquid