Map Man's articles are probably the closest you'll get to a real answer- ATC is a good place also, Damascus and Gorham seem to be decent bets- from there if it's some sort of body study sounds like Hot Springs and Monson would space your brother's study group pretty evenly as far as mileage covered. If the study is related to bodily changes- I would think he might want to include a higher count or a few extra stops early on to study "trail legs". Maybe try to get a 2, 4, 6, 8 week then go monthly from there to help identify some stats on "trail legs". That would be neat info, especially if it covered dietary info.
Maybe Map Man could chime in too-
Here is his table of zero days by % of hikers using them. There may not be as many true zero's in HF- but most stop at ATC even if they don't stay and you can't get much closer to halfway than that really.
http://www.whiteblaze.net/forum/content.php/697
Here is a list of the most popular locations for SOBOs to take zero days. I mention just the places where at least 15% of SOBOs zeroed and list the towns in north to south order (with the percentages for NOBOs listed in parentheses).
Monson ME -- 67% (32%)
Stratton ME -- 28% (15%)
Andover ME -- 36% (15%)
Gorham NH -- 46% (44%)
Franconia Notch NH -- 26% (15%)
Hanover NH -- 41% (28%)
Rutland VT -- 15% (19%)
Manchester Center VT -- 23% (23%)
Dalton MA -- 21% (20%)
Salisbury CT -- 15% (6%)
Delaware Water Gap PA -- 23% (35%)
Duncannon PA -- 28% (27%)
Harpers Ferry WV -- 33% (50%)
Waynesboro VA -- 26% (50%)
Daleville VA -- 31% (38%)
Pearisburg VA -- 26% (51%)
Damascus VA -- 51% (84%)
Erwin TN -- 15% (40%)
Hot Springs NC -- 33% (61%)
Gatlinburg TN -- 26% (22%)
Fontana NC -- 21% (38%)