Unable to set Modified date for files uploaded to SharePoint using FrontPage RPC

Question

When I upload files to SharePoint using FPRC with the following code to set vti_timelastmodified the Modified date shown is always the current date:

 Public Sub UploadSharepointFile(ByVal sSourcePath As String, ByVal sContent As String, ByVal SiteURL As String, ByVal DocName As String, _
                            Optional ByVal sOrigPath As String, Optional ByVal sOrigName As String, _
                            Optional ByVal checkincomment As String, Optional ModDate As Date, Optional FileID As Long)


Dim stream As New ADODB.stream
Dim stream2 As New ADODB.stream
Dim xmlHTTP As New MSXML2.xmlHTTP

    strHeader = "method=put+document%3a12.0.4518.1016" & _
                "&service_name=%2f" & _
                "&document=[document_name=" & Escape(DocName) & _
                ";meta_info=[Original%20Path%3bSW%7c" & Escape(sOrigPath) & _
                ";Original%20Name%3bSW%7c" & Escape(sOrigName) & _
                ";vti_timelastmodified3bTR%7c" & Format(ModDate, "DD+MMM+YYYY+hh:mm:ss") & _
                "]]&put_option=overwrite,createdir,migrationsemantics" & _
                "&comment=" & _
                "&keep%5fchecked%5fout=false" & vbLf

byteArray = StringToByteArray(strHeader)

stream.Open
stream.Type = 1    ''adTypeBinary
stream.Write byteArray


stream2.Open
stream2.Type = 1   'adTypeBinary
stream2.LoadFromFile sSourcePath

stream2.CopyTo stream, -1
stream.Position = 0

'Set xmlHTTP = CreateObject("MSXML2.XMLHTTP")
xmlHTTP.Open "POST", SiteURL + "/_vti_bin/_vti_aut/author.dll", False, UserName, Password
xmlHTTP.setRequestHeader "Content-Type", "application/x-vermeer-urlencoded"
xmlHTTP.setRequestHeader "X-Vermeer-Content-Type", "application/x-vermeer-urlencoded"
xmlHTTP.setRequestHeader "User-Agent", "FrontPage"
xmlHTTP.send stream

If I set a custom date field 'Original Modified' as follows then the correct date appears in the new field

strHeader = "method=put+document%3a12.0.4518.1016" & _
                "&service_name=%2f" & _
                "&document=[document_name=" & Escape(DocName) & _
                ";meta_info=[Original%20Path%3bSW%7c" & Escape(sOrigPath) & _
                ";Original%20Name%3bSW%7c" & Escape(sOrigName) & _
                ";Original%20Modified%3bTR%7c" & Format(ModDate, "DD+MMM+YYYY+hh:mm:ss") & _
                "]]&put_option=overwrite,createdir,migrationsemantics" & _
                "&comment=" & _
                "&keep%5fchecked%5fout=false" & vbLf
End If

Is there a way in can modify vti_lasttimemodified on uplaod to a preset value?

Simon Kravis