How to call a Kotlin top-level function as Apache Camel expression

Question

I am using Apache Camel in my Spring/Kotlin application. Camel let's you call a method on a bean; for example:

.transform(body().method("MyBean", "myMethod"))

How can I call a Kotlin top-level function or extension function instead, where there is no bean that has been registered with Camel beforehand? I am looking for something like .method("myFunction").