There's so many things wrong with this it's crazy.
1) Rippetoe doesn't recommend that you add 40lbs in four months, he recommends that you DTFP. The weight gain is an expected product of the program, if adequate nutrition is used, in the same way that the strength gains are an expected product of the program, if adequate nutrition is used. It should be obvious to anyone that the weight gain you experience on the program will depend on your starting point
2) Any weight gain experienced depends on your starting point. A 140lb 6 foot, underfed beginner could easily add this amount of weight, an elite bodybuilder will obviously not. A skinny-fat 220lb guy of the same height shouldn't make any weight gain with this program. The assumption therefore is that you are eating appropriately for your condition and goals, remember the weight gain IS NOT the point of the program, the strength gain is the point of the program.
3) Rippetoe doesn't recommend that beginners put on massive amounts of weight, he recommends that beginners do the fucking program and use enough common sense to eat accordingly. If you don't like it, don't do the program, no-one's forcing you.