API gateway integration request body to accept wildcard

We would like to apply our model validation to multiple content types in proxy integration with lambda functions. This is without specifying a mapping template. We think it is either achiveable via accepting multiple content type in the request body in "Method Request". Or by rejecting any content type that does not match the specified content types in "Method Request". We have also tried setting the "passthrough behaviour", but as the integration is a proxy lambda integration, it does not validate the request body.