It would probably be better to attend the members meetings of the professional societies that manage such conferences and voicing your objection to Elsevier.
The most powerful boycott would be not to submit papers to Elsevier journals. But given current academic hiring practices this is hardly going to happen, at least not in my field.
German Universities could no longer accept Elsevier papers for hiring purposes going forward. If they did it with 2 years lead time maybe they can tip the scales without punishing the researchers