http://www.jsonline.com/sports/brewers/the-milwaukee-brewers-top-prospects-by-position-b99647931z1-364586871.html
If there is no prospect at first (there was a guy a few years ago who had a cup of coffee at the MLB level, but must have fizzled) why not move Santana to first? He's a big guy, and they have OF depth (and Braun for the next four years) or move Braun to first so he can one hop throws back to the pitcher.
Either way, that spot is set for the next few years.