Have asp.net-hosted WinControl write to client's file.

[Mark]

Hello,
I know that you can host a WinControl in ASP.Net. If I want my Windows User
Control to be able to write to the client's file system (or access a
database, or any other secure action), how could I configure security to
allow this? I thought Caspol.exe or the .Net Config Wizards could do this,
but I don't see how.

I get the error: "The application attempted to perform an operation not
allowed by the security policy. The operation required the
SecurityExcepti on... System.Security .Permissions.Fi leIOPermission. .."

I've tried (none work):
- using Declarative security in the code, i.e. put the attribute on the
appropriate method:
[Permissions.Fil eIOPermission(P ermissions.Secu rityAction.Asse rt)]
- Use .Net Configuration Wizard > RuntimeSecurity Policy > Machine >
CodeGroups. I gave the codegroup the Url to match the page with the
WinControl.
- switching the machine.config' s process model username to system (more
priviledge).
- setting security in IE.

I've googled on the error and looked at MSDN, and see much stuff for apps
run over a network share, but still don't see a solution for an
asp.net-hosted winControl.

Thanks for any insight.
Mark