typescript interface declaration: indexable property

a common use case for javascript objects is to use them as key-value storage... sort of like a dictionary:

var dictionary = {},
    value;
dictionary['key a'] = 99;
dictionary['key b'] = 12;
value = dictionary['key a'];  // 99

typescript intellisense goodness can be added by declaring an interface like this:

interface IIndexable<T> {
    [s: string]: T;
}

and using the interface like this:

var dictionary: IIndexable<number> = {},
    value: number;
dictionary['key a'] = 99;
dictionary['key b'] = 'test';  // compiler error: "cannot convert string to number"
var x = dictionary['key a'];   // intellisense: "x" is treated like a number instead of "any".

here's my question: is it possible to declare a stand-alone version of this interface:

interface StackOverflow {
    questions: IIndexable<number>;
}

ie without using IIndexable?

I tried doing something like this but it doesn't compile:

interface MyAttempt {
    questions: [s: string]: number;
}