Don't use the rule in the first place.
If you are not running adventures league you have great leeway to adapt the rules. Object Vsvs. creature Vsvs. illusion and whatever else is one of the rules ripe for ignoring.
Eldritch blastBlast (as an example) is just sending a beam of force in a certain direction, just let it hit whatever they aim for. Problem solved.
I have always done this and it hasn't caused a single odd situation in my games, in fact it is far more realistic and adds to the game rather than detracts.
Overall whenever you find a rule and think 'this rule is causing a lot of problems' don't then look for more rules to counteract that rule, just ignore it, improvise and move on.