Thanks a lot, it works.
This is what I did, just in case someone looks for the same.
In DonwnloadService I  changed the DownloadData from:
	
	
	
	
	
	
	
	
	
		Type DownloadData (url As String, Target As Object, EventName As String)
	 
	
	
		
	
 to
	
	
	
	
	
	
	
	
	
		Type DownloadData (url As String, Target As Object, EventName As String, PostString As String)
	 
	
	
		
	
 So I added the PostString to the Type
then I changed the
Public Sub StartDownload(data As DownloadData)
where I replaced the J.Download(data.url) with:
	
	
	
	
	
	
	
	
	
		    If data.PostString.Length > 0 Then
        J.PostString(data.url,data.PostString)
    Else
        J.Download(data.url)
    End If
	 
	
	
		
	
 
The call is now:
	
	
	
	
	
	
	
	
	
		    Dim dd As DownloadData
    dd.url = "MyURL"
    dd.EventName = "EventName"
    dd.Target = Me
    dd.PostString = ""  <--- This is now needed
    CallSubDelayed2(DownloadService, "StartDownload", dd)
	 
	
	
		
	
 
That way I can pass an empty PostString to use the HTTP GET but when I pass a Value it uses the HTTP POST.
One thing to note, you need to pass the empty value, otherwise it would be NULL and throw an error.
Maybe it helps someone...