I would suggest 就像真的 is the closest translation. First, it is literally close to "as if". Second, it also has the implication of disbelief.
In your example:
A: 过两年我就开法拉利了。
B: 说得像真的一样 (means 别做梦了)。
"废话!" literally means "redundant utterances". It's the of equivalent somthing like "You bet! [with an unpleasant tone]" which implies you actually agree with him. That's diametrically opposite.