First of all: If your coach wants you to ride a road bike, I suggest he pays for it!
Does he not mean that you should train more on the road? I recently bought myself a cheap second hand road bike, but before, I put 1.0inch slick tires, a road cogset and 48T chainring on my MTB. That worked perfectly, as long as you do not train with guys on road bikes a lot.
There are a few things about your idea... If everything fits, your geometry will be seriously upset. For example: The wheelbase of a real road bike is much shorter than an MTB wheelbase. Also, a road fork would make your front end go down A LOT, even with a larger wheel. It is not a coincident that Gary Fisher's 29er bikes have different geometries than their normal MTB's.
Making everything fit is a different story... you would need an MTB rear hub with a road rim for example. And where would you install the rear road brake on? I do not think the combination of road brakes and V-brake levers works either. You would have to buy Cyclocross brake levers, like froglegs.
I would consider buying a second hand road bike if I were you. The price of one would get close to the cost of converting your MTB! You can put an MTB stem and bar on it if that feels safer and if you do not mind being laught at by roadies
. Do not worry about the strenght of a road frame... if it can withstand Chipollini's sprint, it can withstand yours...