I’m not at my computer, but one way that comes to mind is to create a full copy of the scene. This can be done in the scene controls in the top right-hand side of the topbar. Next to the Workspace tabs. This will create Scene.001. Then invert the gradient (Flip your color ramp) on the material in the new scene. Do a render (F12). Switch back to scene. Then in compositor add a new render layer node and select scene.001 at the bottom. This can be used to give the brighter bloom on the bottom. Then you just need to mask out the Scene.001 leaving the bloom. You might be able to do this by turning on transparent in the render setting of Scene.001 and then use an invert node on the alpha channel. Then just combine the bloom with a mix color node using the alpha as the factor. I’ll have to play with it when I get home from work.
***Edit*** You might want to play with the setting under highlights on the Bloom node before trying the above. This will allow you to clamp the brightness of the bloom while lowering the threshold. This keeps the Bloom in a more even color when you have such drastic brightness level if I’m remembering correctly.
