Yeah, you will need to prerender to a texture first. Here's what i would do:
- Prerender an object to texture.
- Downsample multiple times to a desired size (more downsamples = bigger glow).
- Apply some kind of blur (I prefer Gaussian).
- Tint blurred texture with some color.
- Upsample.
- Render.
You can take a look at the example I posted in my blog. It's for Alternativa3D but may be useful as the principle is the same everywhere. Here's github link to whole lib.