The Deconstruct Dimension component is not intended for the actual lines, etc. of the annotation, it’s reporting the points and planes that were used to construct it.
Since eleFront is just creating a thin wrapper around the rhino type, you can indeed use the Explode function in RhinoCommon, once you cast the object to a Dimension type:
var annotation = (Dimension) x;
a = annotation.Explode();