Bryan your last comment is exactly what I just sat down to post about. Some people seem to have a problem with "absence of pain" because they refuse to separate out the parts of the body, which you just pointed out is important to consider. They want to say that "I" am in pain whenever their foot or their stomach hurts, as if there is some abstract "I" that is the sum of all the separate feelings from all the separate parts of the body and mind, and that they should ignore the entire rest of their mind and body that is not in pain.
While we do have a consciousness that can shift its awareness from one part of the body to another, or to multiple parts at once, when we are talking about pleasure and pain we are really talking about the parts of the mind or body that are involved, and we are considering the duration and intensity of those pleasures in the different locations.
We can have a headache, but our little finger at the same time is not in pain. Epicurus is telling us to think about the big picture but not to lose sight of the fact that you can do more than one thing at once. Just like Epicurus did at the end, you can offset the pleasures of thinking about pleasant things against the pains in other parts of the mind and body. You can't erase the pains from existence by doing so, and if they hurt bad enough then you're definitely going to feel it, but you can offset them against each other when evaluating your overall existence.
I would say that the point Epicurus seems to be getting at is that we are not some disembodied "unit" where we are either "in pleasure" or "in pain" as a unit. We are real living things with different parts of our minds and bodies, and just because our little finger is hurting that does not mean that our entire existence is controlled by that pain.
This comes to mind too because this is covered in why "absence of pain" is not a "fancy pleasure" (Elayne's term in her article). A peanut without salt is a peanut. Any specific pleasure without accompanying pain is still that same specific pleasure - not something new. When we stipulate that someone is experiencing life "without any pain," what we mean is that the person is experiencing life - the same combination of pleasurable experiences that existed before that last unit of pain was removed - not entering some kind of state of transcendental ecstacy or euphoria.
I think your bringing this up is extremely helpful both to the "Bursting the Gate" article and Elayne's "Pleasure Pain and Happiness" article. The Bursting the Gate article focuses more on what Epicurus/ Torquatus "were" saying, and the "Pleasure Pain and Happiness" which argues against "Fancy Pleasure" is focusing more on what Epicurus "was not" saying.
Both perspectives require this understanding that "absence of pain" doesn't mean the creation of some new type of experience. If I recall correctly, this is where Gosling and Taylor end up in their long article on katastematic pleasure in "The Greeks On Pleasure." There are definitely all sorts of mental and physical pleasures, but "absence of pain" does not constitute a pleasure of its own unique type. There are numberless types of pleasures and pains, but in the end we come back to the understanding that there are only two feelings, pleasure and pain, and "absence of pain" is just another term for "pleasure." Epicureans reason by analogy from their own experience to those things which have not yet been observed by them, they don't let loose of reality and all of a sudden then that getting to 0% pain transports us to another dimension (as implied by those who talk in low voices about "absence of pain" in a Buddhist-like sense).
Both "pleasure" and "absence of pain" can be used to describe the same numberless set of ordinary agreeable experiences with which we are all familiar, and neither describe any separate and special experience that is outside the term "pleasure" and available only to the gods, or available only to the person who hypothetically reaches a state of "total absence of pain." As I think we've discussed on the forum before, there's no reason at all to think that there is a major change in condition between the person who is experiencing 99.9% pleasure / .01% pain and the person who is experiencing 100% pleasure and 00% pain.