В итоге я извлек его из папки .svn в текущем рабочем каталоге.
var httpAddress = getHttpAddress(WScript.Arguments(3));
function getHttpAddress(currentWorkingDirectory) {
var entriesFile = currentWorkingDirectory + "\\.svn\\entries";
var fso = new ActiveXObject("Scripting.FileSystemObject");
var file = fso.OpenTextFile(entriesFile, 1);
var line = file.ReadAll();
file.Close();
var pieces = line.split('\n');
for (var idx = 0; idx < pieces.length; idx++) {
//pretty cheap, but we just loop till we find a line that looks like a url
if (pieces[idx].substr(0, 7) == "http://") { return pieces[idx]; }
}
return "";
}