almost same as the first one a gave you. just give it a bit smaller particle size and set alpha for start to 0, mid to 255 and end to 0. This should make it not appearing at start, forming a circle like effect. Oh and activate line emiter too
Now that I think about it some more, an even sneakier way to do that, would be to use an animated texture (take a look at clouds8x8.blp in textures if you've never seen this before). An advantage to doing this would be the ability to have as abrupt a fade as you'd like (or even multiple fades)