Although the butter does become integral to the egg and therefore affect the taste it's primary function is to lubricate the egg whilst it is cooking. Therefore an oily spread would do but I don't think it would taste as nice.
You melt your knob of whatever in the pan, beat the eggs quickly with a fork but not too much, then add the eggs (diluted or otherwise) to the pan when the whatever begins to bubble and continue to stir throughout the cooking time, you should remove the eggs from the heat just before they become solid to prevent overcooking.
If you do use liquid you should use only a tiny amount, a dessertspoonful?