Because the reflected Suzanne is not an object in the scene, it can’t be directly “extracted” using Render Layer methods, so you’ll have to use some sort of matte-generation/keying method. A Render Layer (RL) of just the reflecting object should be enough to separate the reflection from everything else except the surface that’s doing the reflecting. You can then pull a matte from the reflected image using a node like Luminance Key. This can be used to isolate the reflected image and give it the same blur treatment as the actual object.
If your objects are hard to pull mattes from due to materials and/or lighting, then you can use a proxy on a separate, non-rendering layer. This proxy could be matte black or flat white – its only purpose is to generate a matte element – and it should match the real object exactly in terms of animation. The idea is to produce a matte plate that can then be used to modulate/mask/filter the other nodes as needed to get your reflected glow.
If you’re into movie history, this is a digital analogy to the method used by Douglas Trumbull in both 2001: A Space Odyssey and Bladerunner to generate a lot of the optical mattes for the model work. Models were shot with motion control in multiple passes, some of which had the models covered in white tape to pull high-density mattes off them.