There is a procedure being used in traditional old-school qualitative analytical chemistry, the shit you are bothered with first at the local universities since it frustrates so many wanna-be chemists that many will quit voluntarily.
When you want to identify the anions of insoluble inorganic compounds mix them with an excess of Na2CO3 and some water, heat for a while, filter the insolubles out and perform your tests on the Na2CO3-solution. Since carbonates of most metals are usually very much insoluble it is possible to convert not-quite-as-insoluble-but-still-hardly-soluble metal compounds into the carbonates, leaving the anions as the sodium salts which can be easily identified by standard procedures.
Sounds kinda confusing? Ok, here's an example: We have an inorganic sample believed to contain PbSO4, which is pretty much insoluble in water and therefore can't be easily analysed. Since PbCO3 will be several magnitudes more insoluble the very slight solubility of PbSO4 will be enough to convert part of it into the carbonate:
PbSO4 + Na2CO3 --------------> PbCO3 + Na2SO4
After filtering out the Pb salts the Na2CO3 mixture is carefully neutralised with a suitable acid, and the SO4(2-) can be detected by standard reactions, e.g. forming a precipitate with barium nitrate solution.
(If this PbSO4 example happens to be an exception which does not work then I'm sorry, but I guess you got the idea)
There's only one problem: this whole thing doesn't go anywhere near completion in a realistic timeframe, and when decomposing CuCN with Na2CO3 (or NaOH, which should work just the same, it all depends on molar saturation concentrations) you will end up with a mixture of lots of Na2CO3 (/NaOH) and a little bit of NaCN, which is probably completely unusable for your intended reaction.
I'm not fat just horizontally disproportionate.