SSRS - Is there a multi thread safe way of displaying information from a DataSet in a Report Header?

 In order to dynamically display data in the Report Header based in the current record of the Dataset, we started using Shared Variables, we initially used ReportItems!SomeTextbox.Value, but we noticed that when SomeTextbox was not rendered in the body (usually because a comment section grow to occupy most of the page if not more than one page), then the ReportItem printed a blank/null value.

So, a method was defined in the Code section of the report that would set the value to the shared variable:

public shared Params as String

Which would be called in the detail section of the tablix, then in the header a textbox would hold the following expression:

=Code.Params

This worked beautifully since, it now didn't mattered that the body section didn't had the SetValues call, the variable persited and the Header displayed the correct value. Our problem now is that when the report is being called in different threads with different data, the variable being shared/static gets modified by all the reports being run at the same time. 

So far I've tried several things:

- The variables need to be shared, otherwise the value set in the Body can't be seen by the header.

- Using Hashtables behaves exactly like the ReportItem option.

- Using a C# DLL with non static variables to take care of this, didn't work because apparently when the DLL is being called by the Body generates a different instance of the DLL than when it's called from the header.

So is there a way to deal with this issue in a multi thread safe way?

Thanks in advance!