This functionality has been implemented as MNG-5768, and is available in Maven 3.3.1.
The change will:
extend direct plugin invocation syntax to allow optional @execution-id parameter, e.g., org.apache.maven.plugins:maven-remote-resources-plugin:1.0:process@executionId.
So, in your case:
mvn antrun:run
uses the default-cli
execution ID, and:
mvn antrun:run@my-execution
uses the execution configured in your pom.