According to the documentation for STAThreadAttribute, you can not have more than one thread that is STA (you can't even truely have one unless you are using COM interop).
"Apply this attribute to the entry point method (the Main() method in C# and Visual Basic). It has no effect on other methods."
Since .Net 2.0 the Single Threaded Apartment is only intended for use when performing COM interop.
"COM threading models only pertain to applications that use COM interop. Using this attribute in an application that does not use COM interop has no effect."
"In the .NET Framework version 2.0, new threads are initialized as ApartmentState.MTA if their apartment state has not been set before they are started. The main application thread is initialized to ApartmentState.MTA by default."
Reference: http://msdn.microsoft.com/en-us/library/system.stathreadattribute(v=vs.100).aspx