Use the InvocableVariable annotation to identify variables used by invocable methods in custom classes.
Here is the text of the email I received back from Salesforce:
Your salesforce.com request to convert a lead into the following records has successfully completed:
Account: Blues Entertainment Corp.
Contact: David Monaco
Opportunity: Blues Entertainment Corp.
InvocableVariable Annotation - https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_classes_annotation_InvocableVariable.htm