How to scan additional digits on EAN13? (EAN13+2)

I've been running the PsionTeklogixDemoApplications demo solution provided with the Mobile Devices SDK V3.4.

(C:\Program Files (x86)\Psion Teklogix\Mobile Devices SDK V3.4\Samples\dotnet\VB.NET2005)

I'm running this from Visual Studio 2008 (I upgraded the demo solution first) and deploying it to a Psion NEO running Windows CE 5.0.

"Out of the box" the Scanner test is scanning in EAN13 digit barcodes, but we would like to also be able to scan in EAN13+2 barcodes, an example image is attached. (Sometimes EAN13 can be referred to as "EAN15" although I don't know how common that usage is)

We've tried changing the properties of the scanner as follows, modifying the sample code to add in the extra lines as below:

' btnDisableScanner_Click - event handler
'
Private Sub btnScanner_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnScanner.Click
Me.ScannerServicesDriver1.SetProperty("Barcode\EAN13\HHP\2 Digit Addendum", 1)
Me.ScannerServicesDriver1.ApplySettingChanges()

MsgBox(Me.ScannerServicesDriver1.GetProperty("Barcode\EAN13\HHP\2 Digit Addendum"))

Me.Scanner1.Enabled = True
End Sub

We've tried several of the settings, but none of them seem to turn on EAN13+2 scanning, the first 13 digits are scanned but the last two digits aren't.

Barcode\EAN13\Imager\Addendum = 1 (didn't work)

Barcode\EAN13\Addendum = 1 (didn't work)

Barcode\EAN13\HHP\2 Digit Addendum = 1 (didn't work)

Any ideas?