I have seen people do this, but really, I wouldn't send one person ahead, it won't really give you that much of a head start, there are people that run the second the gates open, since they no longer let you on main street early, there is no rope drop anymore, when they did do that they would even occasionally open the Main Street Opera house early, then I would have said go and see that, then you can enjoy the rest of the park, but really it's not worth it, you will only gain about an extra 5-10 minutes and in some cases (such as what happened to me once, where a person in an ECV ran over my foot because I wasn't moving quickly enough for her because there were people in front of me) you may even loose time that could be spent on other rides.
For the record I have no problems with people in wheelchairs or ECVs and I go to great length to make sure that I am not in their way, even though my mobility may be more limited than some other peoples, I am able to get out of the way of a ECV or Wheel Chair much easier than the person in that wheelchair or ECV can move out of my way.