In reply to Axel Smeets: We've just spent the morning fitting Yetis to Scarpa Vegas and La Sportiva Spantiks and now have sore fingers. We did get the technique sussed though, as follows....
Before you start, get a hairdyer and heat the rubber until it's nice and supple.
Put the toe of the boot in the gaiter and pull the rand over until it sits in place, the bottom of the rand on the crampon toe welt.
Next, pull the middle section f rubber over the sole until it sits in the middle of the sole between the toe and heel grips. This bit is a bit harder.
Next hook the thin rubber strip between the sole grips as tight as it will go.
Now for the hard bit. We had two people so it made things a bit easier. Pull the heel rubber as hard as you can until its strateched level with whee you want it. Then stick a woode spoon through between the gaiter and boot to hold the gaiter in place. You'l end up with a fold of material so you need to pull this straight, then use the spoon to force the gaiter into place. It takes a bit of effort but it does work - I justhope I've explaned it well enough!