I am not too sure how good of an idea that would be. Technically there is a Dura-Ace front derailleur designed for a triple crankset. But, the new Dura-Ace derailleur is designed to be used with a 10 speed system (narrower chain I believe) and a crankset with a 52 tooth large chainring. If you were to install the derailleur, the cage would not follow the contour of the crank correctly. This will result in the chain not being positioned over the contours in the cage when trying to shift resulting in poor shifting or possible jamming. Also, you may have the chain rubbing on the derailleur cage in certain gear combinations due to where the derailleur is realtive to the chainrings.
This next part I am not 100% sure on but I believe the indexing of MTB front derailleurs is different than that of road front derailleurs too. When Shimano designed components for the flat bar road bikes they needed to make new rapid fire shifters just for that purpose.
This next part I am not 100% sure on but I believe the indexing of MTB front derailleurs is different than that of road front derailleurs too. When Shimano designed components for the flat bar road bikes they needed to make new rapid fire shifters just for that purpose.