There are lots of ways people raise money for charity, usually involving some physical endurance, such as walking from LA to New York, climbing the three highest peaks in Africa, or cycling from the Panama Canal or Tierra del Fuego. With each of these, there is an element of hard work and endurance, in addition to being somethig not many people can claim to have done.
Not to discourage you, but where are those factors on your 'round the world trip? The antipodes would certainly add something, but a somewhat straightforward BOS-LHR-BKK-SYD-LAX-BOS (which you could do purchasing a oneWorld RTW ticket) doesn't seem to provide the "endurance" element. How are you going to up the ante to make it appear more of a sacrifice or physical endurance? That may do well to bring on more attention.
Might I suggest that you insist on a middle seat in the middle section of each widebody flight, and middle seats for narrowbody flights? Not in business class, or World traveller plus, but the back of the bus, in the economy section. Make sure (in fact demand) the person in front of you recline all the way, and make sure that your inflight entertainment system is malfunctioning. And at least one or two of those flights there should be a delay on the tarmac resulting in time waiting for weather to clear.
