The current document is directed to methods and systems that that generate proxy-object interfaces to external executable code for use in workflows executed by a workflow-execution system. The workflow-execution-engine component of a cloud-management system provides one example of a workflow-execution system in which proxy-object interfaces to external executable code are used. In one implementation, an existing automated-code-generation subsystem generates plug-in class declarations that represent one or more external executables. An additional class-wrapping subsystem then generates a proxy class for each code-generated plug-in class.