Accessing QualifiedName or SOMExpression in a custom rule function

We are developing a custom function to update the values of several fields depending on some logic. 

We would like this to be configurable through the Rules Editor so that the fields can be dragged onto the Input parameters.

However we seem to be unable to get hold of the field Object directly or pass in either the QualifiedName or SOMExpression (we are using Core Components, hence the QualifiedName) - All we can get is the value of the field.

I had also though we could try getting the QualifiedName from a property and passing that to the input for the custom function.

Has anyone got any suggestions?

We used to be able to access the SomExpression from the Rules Editor but not in the Cloud / Core Components setup