How do I do a regex query in reverse in entity query?
Okay, is seems like this is in fact impossible to do right now with config entities.

If you look at \Drupal\Core\Config\Entity\Query\Condition, and into the function match, it shows what operators are available for config entity queries. REGEXP isn't even an option. Nor is there anyway to query a value against a field, instead of a field against a value.

The only way to really do this seems to be to load all of the config entity records into memory, then do the comparison with php.