Aaah! But where is the squeak?
It's not necessarily in the poly or whatever the bushes are made of. The squeak is either between the bolt and the inner metal sleeve of the bush, or it's between the poly and the outer metal bush, (or the wishbone itself of course as there is probably no outer metal sleeve of the bush itself).
If it's the former then you have to withdraw the bolt and lubricate it with coppaslip or some such.
If it's the latter then red rubber grease (which is the same as no-crode for battery terminals) will keep it all quiet.
Of course using Nylatron is an even better idea.
No inner metal sleeve employed when these are made I assume?