Service Activity - set properties using variables

Is there any way to set some of the properties of a Service process step by using a C# code block prior to the Service process step, or by using environment variables (or other types of variables) for the values and then populating those variables?

For example, I want to dynamically set the MetaDataUrl, Servicename, and the Action properties on my Service process step?  I can either do this in C#, or by setting the values for each of those to a variable.