Here's a quick and dirty how to. If I had surviving layers I'd shoot them to you but they've all been flattened and merged to allow me to do composite outlining.
First, go to
Slagcoin and pick a layout if you don't already have one. I'll assume you're working in Photoshop since you mentioned it.
Import the outline you chose (if you don't already have one) and ensure it's to scale for your resolution. Everything he has is sized at 72dpi I think so if you're working in 300 you'll need to blow it up and use the rulers to ensure you're spot on.
Now, take the shape tool and select the circle. Size yourself a circle that gives a ballpark halo for what you're wanting. This will be a vector shape so all the color adjustment needs to be done from the drawing menu and not working with the object as you would a regular layer. If you don't feel comfortable eyeballing things once you start moving them around you use the ruler guides to split the circle in quadrents and then put another tiny circle at the intersection, preferably in a contrasting color.
Link those two layers. You now a have single circle with a good center. Set it to about 25% fill and move it over the button overlay you imported. Once it's over the first button resize the halo until you get what you want. Then you can duplicate the layer and move the dup over the second button. Lather rinse repeat. Once you've covered everything the way you want it and centered it all bring the fill back up to 100%. If all your circles intersect you can rasterize all those layers (I assume you're not working in vector) then merge them all into a single layer (I do this by button sets initially) then you can use the stroke option in layer properties to outline the set. If the circles don't intersect you can then use the oval tool and make another vector shape behind all your buttons and move it around till it makes you smile. Then rasterize and stroke. From there it's a matter of color and opacity to get the effect you're looking for.
Send me your CP and I'll do a set that you can then copy and work with. Nothing like learning on your own art. PM me if you're interested.