1) make sure your friend knows what you are wearing...other than a your kiddo
2) You will be standing for periods. Get an idea of their pace so you know when to expect them along the course. You will need to know their corral and start time - both will be known near the race.
3) the better places to watch the half are
a) near the TTC(mile 4.2). My DW selects a spot just at the ramps.. but there is a good quarter mile of course you can stake out. Just make sure to be on course left or the Poly side of the course. Once the mass of the race comes through you will not be able to easily cross.
b) after the TTC, walk to the Poly/GF(Mile 7.5) and watch them pass again.
c) after the Poly/GF, monorail back to Epcot to catch the finish.
Hope this helps. Again, make sure they know what you are wearing and you them. Also, if they know kind of where you will be, then most likely they will find you are they pass.