Is it really that big of a deal to get a little head start? I could see having issue with someone getting towed up to speed by a car or something but that's not the case, they're using the same steep descent that is available to anyone else right?

If you're still bothered by it create a new segment that starts halfway up the hill until you reach the top. That way any effect an initial starting speed had is gone and you have a segment that is all leg power.