Join Date: Jan 2000
Location: Steelhead country|striper coast|bonefish belt
1) Generally speaking, no. The ideal length of line to form a d-loop is not really benefitted by slipping line into it because it increases the tendency for the loop to lose it's tension, which is key to loading the rod for the forward stroke. I suppose it's possible but would introduce additional complexity to the whole affair. Maybe there's someone out there who does that, if so I defer to them.
2) When using the snake roll, the position of the anchor and the direction that the top half of the d-loop is pointing defines the proper direction for the forward cast. Therefore if you coil the spiral so that the anchor lands with an upriver angle and the d-loop forms fully with the top half pointing toward an upriver target, it's possible to cast upriver with a snake roll. Generally for the common river presentations used with spey rods this is not done. Swiveling the body during the snake can greatly increase the upriver angle. Some expert casters are able to do 180 degree single speys, so a snake roll with a huge angle should be cake for them. I've never practiced anything more than 45 degrees upriver myself so am not the best one to answer.
Welcome to the spey clave.