As Niles says, considering 29ers are just MTBs built on 700 C rims. It is certainly feasible, the issue is whether the weight is worth it. I have always managed on 1.5" tires, normally slicks. But it doesn't take much imagination to come up with conditions requiring a lot more tire. I just don't have extended off-road touring options around here. For a mostly road bike I prefer easy rolling tires, and I get by by releasing tire pressure in sandy conditions. I have reduced pressure to as little as 25 pounds.