We could more or less do that now. In fact we should probably just stop growing corn for biofuel, it's not obvious that it's even energy-positive, let alone a good use of farmland.

What do you mean by Biofuel? Like getting it from Biomass.

I don't understand, can't we get Biomass from like undesirable items like (not to gross anyone out, but feces?) whereas corn still has some value where you can actually eat it.