Extend existing class by delegating to a specified object?

Is there a way, either currently or with anticipated features, to extend an existing class by delegating the members of an interface to a specified object?

I can declare a new class that delegates to a specified object, i.e.

class IntervalRange(interval: Interval) : ClosedRange<Int> by interval.a..interval.b

And I can extend and existing class by individually delegating members to a specified object, i.e.

operator fun Interval.iterator() = (a..b).iterator()

Is there a way to delegate all of the ClosedRange<Int> members to a..b? Something like,

Interval : ClosedRange<Int> by a..b