A rad idea... Unless you NEED the additional range of multiple chainrings, omit the front derailleur entirely! With today's wide-range rear derailleurs, more and more bikes really don't need the multiple chain rings at all. Additional reliability can be had with cyclocross type chain guards, and the chain line is less complex with a single front ring. The bike is cleaner, lighter, and simpler without the complication of multiple chainrings.