I wouldn't worry about that. I've poured hundreds of gels and added the EtBr to it after microwaving it every single time. Never had anything close to that happ

I wouldn't worry about that. I've poured hundreds of gels and added the EtBr to it after microwaving it every single time. Never had anything close to that happen. Just use a sufficiently concentrated EtBr stock and you're adding like 45 µL to 45 mL.