Updating a process schema parameter with client-side code

I'm having some issues with updating the value for a parameter from client-side code, from the ProcessSchemaPropertiesPage (process designer).  The reason for this is that I have a base process that is getting coppied for a specific use, and I'm passing a value to that copy that should be saved to a process parameter.  I need to reference this parameter from a process execution.

What I've attempted is this:

             saveValues: function() {

                    process = this.get("ProcessElement");

                    var scope = this;

                    var parameters = process.parameters;

                    Terrasoft.each(parameters, function(){

                        var item = this;

                        if(item.name == "marketingProcess"){

                            item.sourceValue.displayValue.cultureValues["en-US"] = "test123";

                            //item.sourceValue.value.cultureValues["en-US"] = "test123";

                            item.sourceValue.value = "test123";

                            scope.saveParameter(item); 

                        }

                    });

                    this.callParent(arguments);

               }

It looks like it works, but it's not actually updating the parameter value.  I've tried something similar on the loading of the process and on saving.

Any ideas how you can manipulate process parameter values client side?  I would even be willing to use a server-side solution, if one exists.  I've looked at the server-side process services and I'm not seeing anything obvious there either.

Any ideas!

Thanks!

Jeremy