Firstly, if you don't do most of the sidequests and stuff, it's WAY under 40 hours. It's really not a very long game if you just go through the plot. As to the difficulty setting, I can't say I really agree with you, but tis a matter of opinion. For me, Mass Effect is a game of story, and world. The gameplay is fun, but if you play the first game for X hours followed immediately by the second, you're going to get sick of the gameplay, for sure. Or at least, I personally would. *shrugs*

I recommended easy because it would quickly bring him through the high points of the first game, and then let him spend the bulk of his time on the second one, which is the more deserving. I just don't think someone would have the motivation to play through everything there is to do in both games, back to back. I say play the first one quickly as an intro, and then immerse yourself in the second.