How do I work with cascading report param in ReportExecutionService?

I'm using ReportExecutionService in my app.

I am working with cascading params. For example, companyID decides the list of custom params that are specific to the company

What I want to do: 1. load rpt by url; 2. get params; 3. set companyID; 4.send to rpting server; 5. get back params specific to the companyID that i passed in; 6. set the custom params that's specific to the company ID; 7. send to rpting svr for rendering.

How do I achieve this?

Thanks in advance.