Well, if you know of a common sense way to resolve this issue without (a) creating a rule that would be easily gamed, (b) coming up with a completely arbitrary rule that has nothing to do with what’s good for the country, or (c) leaving it up to the unpredictable whim of IRS bureaucrats or tax judges, I’d be interested to hear it.
The truth is that there is no way to implement Santorum’s proposal that wouldn’t provide a lot of work for lawyers. Even though I am a lawyer, as a citizen, I don’t want that kind of system.
Since you are a lawyer, I doubt you could accept common sense answers. The easiest idea to dispel with is the notion that anyone pays a tax other than the person who produces the wealth. If you can grasp that concept then you may be open to the idea that tax lawyers are not indispensable.