Just in case anyone else was having troubles with this:
I don't know if what I found existed back when this question was asked, but I found a script that comes with Unity, called "Outline", which gives text a kind of glow or halo effect. It's found under Component > UI > Effects > Outline. Set the colour of the effect, and then set the "Effect Distance" X and Y properties of the script to how much you want the effect to radiate out from the text.
It may not give the best effect, but it worked well for what I needed.
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