I would imagine this is entirely plausible. Males are the determining factor regarding the sex of their offspring since females only have one gene (X) to contribute and males have two (X & Y). Also there are many family lines which produce an abnormally high amount of females or males. So I guess it is possible. There is much much more to this such as genetic abnormalities of males that have XXY and XYY that could tip the scales towards more female and more male sperm and many other factors to consider as well but lets not get into all that. Dont know it works like this with snakes but it does occur in other species such as humans.