Why not just use WSUS?
That is what MS is using to distrubute it anyway, and you should be up to that by now in any case.
That said, I think that trying to convert any windows update into an MSI is a mistake. You risk getting something wrong, and possible effects to the machine are everywhere. I would look for another solution to this.
One you might look at, if you can't distrubute any other way, is simply creating an MSI that runs this install. That way, you are not breaking anything that MS want's to install. As far as I know the only application that you can use for free is ORCA.