The recipe in Ruhlman's book is basically a beef sausage flavoured with foie, sweetbreads, bacon, mushrooms... it's a bit of a dog's breakfast. Not recommended.
If you want to taste the expensive foie gras instead of grinding it up with a dozen other ingredients (which, to me, defeats the purpose of the exercise), make a torchon. Ruhlman has a recipe on his website
http://ruhlman.com/2011/05/how-to-make-torchon-recipe/
taken from the French Laundry cookbook, complete with the same error as in that cookbook - "sodium nitrite" should read "#1 curing salt". This kind of sausage doesn't keep very long; think of it as a foie pate in a tube shape.
The Robuchon recipe that Martin links to above sounds good as well. I'd be tempted to add a bit of #1 cure to it as well, for colour. Google Translate does a good job for those of use who aren't cunning linguists:
http://translate.google.com/translate?h ... e-gras.htm