I don't know anything about clothing, but I have investigated the assistance issue in regard to a trials attempt. Basically, it's against the rules (IAAF/USATF) for anyone, excluding a race volunteer or official, to hand you anything during the race. However, a coach or friend can set out for you -- at a designated aid station -- something for you to pick up yourself. (This is why even elite athletes have to grab their water bottles themselves at major races, though sometimes you do see them getting help (from volunteers?))
Anyway, if your race doesn't have separate tables for elites at the aid stations, just have someone set out your stuff at some pre-designated location at whatever aid stations you plan on using --i.e. the last water table on the right at Miles A, B and C, or whatever -- and mark your water bottle or whatever in some way that makes it VERY easy to spot and pick up.
It would also be a very good idea to coordinate this with the race director and aid station leaders for whatever aid stations you plan on using. Unless your race is very big, they'll probably be more than happy to help you out.