There's no way to do this - while Scope's have a Parent property ScriptScope's don't expose this. The parent property on Scope's is also going away. If you want to chain lookups you should create a ScriptScope w/ your own custom IAttributesCollection which knows how to look in the parent scope.
Thank you.I found I could create a Scope with a parent scope using Scope(Scope parent, IAttributesCollection dictionary), and HostingHelpers can create a ScriptScope from a Scope.