I was working on this problem just the other day at my local shop. With the basic eggbeaters, there's nothing except zipties, and even that doesn't work well because you can't keep the strap on the underside of the pedal -- it still will tend to turn 90 degrees, at which point the strap is trying to pull off the pedal rather than up into it. With Candy's, it's much easier -- the strap attaches to the frame with existing hardware.
All this begs the question of ... why? It's not a pedal designed or intended for ultimate clip-in security. It's not even a particularly good platform for high power high rpm riding -- its strength is in off-road and in certain road situations. This isn't to demean Eggbeaters in any way -- they are a great design -- but you are looking to make an apple taste like a steak. Get a different pedal and you'll be much better off if toe straps are what you really need.