Instead of using asInterfaceInstance, you may use a class augmentation which is described later in this documentation. In short, it allows you to call a to method on instances of MethodHandle, which in turn calls asInterfaceInstance. Back to the previous examples, the next 2 lines are equivalent:

# Calling asInterfaceInstance
future = executor: submit(asInterfaceInstance(Callable.class, -> "hey!"))

# Using a class augmentation
future = executor: submit((-> "hey!"): to(Callable.class))