No, there isn’t. If it’s in that format, then it’s not a valid dateTime as far as XML Schema is concerned.
The best you can do is as follows:
[XmlIgnore]
public DateTime DoNotSerialize {get;set;}
public string ProxyDateTime {
get {return DoNotSerialize.ToString("yyyyMMdd");}
set {DoNotSerialize = DateTime.Parse(value);}
}