Error Output For A Destination Transformation

I am developing a custom destination component and I have encountered a few areas where there seems to be a lack of helpful documentation and examples.

1. I have not been able to find any information on or examples of creating custom destinations with an error output. The OLE DB Destination has an error output so I investigated the input and error output properties in the advanced editor and found that the OLE DB Destination error output is synchronous with the input (its SynchronousInputID matches the input's ID) and has its ExclusionGroup value set to 1. Using this information, I modeled my error output after the OLE DB Destination.

ProvideComponentProperties:
AddErrorOutput(ERROR_OUTPUT_NAME, input.ID, 1);

ProcessInput:
int errorOutputID = -1;
int errorOutputIndex = -1;
GetErrorOutputInfo(ref errorOutputID, ref errorOutputIndex);
...
buffer.DirectErrorRow(errorOutputID, 0, errorOutputIndex);

Checking the input and error output properties in the advanced editor for my custom destination component I find the following:
Input
-----
ID: 3515

Error Output
------------
ExclusionGroup: 1
ID: 3516
IsErrorOut: True
SynchronousInputID: 3515

Shortly after I start my SSIS package and it encounters an error row, I get the following exception:
[My Destination Adapter 1 [3512]] Error: System.ArgumentException: Value does not fall within the expected range. at Microsoft.SqlServer.Dts.Pipeline.Wrapper.IDTSBuffer90.DirectErrorRow(Int32 hRow, Int32 lOutputID, Int32 lErrorCode, Int32 lErrorColumn) at Microsoft.SqlServer.Dts.Pipeline.PipelineBuffer.DirectErrorRow(Int32 outputID, Int32 errorCode, Int32 errorColumn) at MyDestination.ProcessInput(Int32 inputID, PipelineBuffer buffer) at Microsoft.SqlServer.Dts.Pipeline.ManagedComponentHost.HostProcessInput(IDTSManagedComponentWrapper90 wrapper, Int32 inputID, IDTSBuffer90 pDTSBuffer, IntPtr bufferWirePacket)


2. My custom destination component is used for writing a file with a fixed schema. I followed the means by which source component examples add their output columns, but applied this to my external metadata columns. In my Validate() I check if the ExternalMetadataColumnCollection.Count == 0 and return DTSValidationStatus.VS_NEEDSNEWMETADATA; to force a call to ReinitializeMetaData(). In ReinitializeMetaData() I call a method that creates the input's external metadata columns that reflect my external data source.

This works fine except every time I add my custom destination component to a SSIS Package and go to edit the component I am greeted with a dialog box that states: "The component is not in a valid state. ... Do you want the component to fix these errors automatically?" Pressing the Yes button, I assume, makes the call to ReinitializeMetaData() and I have my external metadata columns. Where is the correct place to add the external metadata columns so the user does not have to take this extra step every time they add my component to their package?