Most of the "real" solutions are designed to be used from the Blender Internal Renderer or Cycles, not from the OpenGL Preview. You can still do it with the OpenGL Preview, but I'd really recommend using BI to get the look you want. It's going to provide you A LOT more functionality for compositing, editing, and effects.
Your best solution is going to be a compositing approach. This is the way it's done ;-) What you need is an object-specific mask, which you can produce by rendering out an "Object Index" pass. You'll have to specify how you want to get this pass.
- You could render it out without any other passes selected, which would work a lot like a regular render. You'd get a psychedelic version of whatever frame you were rendering (more on that in a minute).
- You could render to OpenEXR, which will save each of the passes separately, but in one file per frame; then you'd bring the EXR into the compositor and the input node will have a spot for "Object Index" as well as any other passes you rendered.
- You could set up compositing nodes with separate "File Output" nodes for each pass that you want. This would give you individual files for whatever you wanted (like individual passes), and you can save them into their own directories, or whatever.
Once you have this Object Index pass, you can modify it (in Blender using compositing nodes or in another tool like AfterEffects) into a mask for whichever object you need. The Object Index pass looks like a psychedelic version of your scene. Each object is given its own unique color, and then rendered without any shading at all. You can modify that into a b/w image that masks out the one (or more) object you want. Then you use that mask to composite in whatever effect you're trying to produce. You can even use the same image to produce several masks for different objects.
The other approach is to use Render Layers. Move an object that you want masked out to another layer from everything else. Then select that layer in the "Mask Layers" section of the Scene settings, and you'll get a render with a "hole" where that one object is. You can then pretty easily convert that image into b/w which you can use as a mask to do your effects in Blender, AE, or whatever compositor you're using.
Do some research on Render Layers, Mask Layers, and Object Index, and I think you'll find what you need.