http://www.jannsnetcraft.com/fly-tying-eyes/650200.aspx
Here's another option more specifically for flies.

I have not used wiggle disks on flies though I have used fly rod Flatfish for, let's say, a long time. As you might suspect the extra resistance and bulk of the bill or wiggle disk is best countered by beafing up the rod. It is a chore to pull the Flatfish free of the water, but one is compensated by the excellent way it loads the rod for the backcast.

Though I prefer to use simple flies, I will tie on whatever it takes.