Brake squeal as I understand such things results from one or both brake arm assemblies resonating while under braking load. The objective is to change the system in some way to move the resonant frequency out of the range encountered in normal operation. One thing I've (apparently) had success with is using a thick (eg wheel-bearing) grease on the pivot bosses. If there has been enough wear to allow "rocking" movement of the brake arm, the grease may provide some damping. Might be worth a try.
(Greetings from Mundelein!)