Numbers 'Fill Series' between start and end point

Is there 'Fill > Series' equivalent in Numbers? I'm looking to fill in blanks in equal increments between the start and end point of a series e.g filling in each of the other letters using only A .... Z. I know I can autofill having filled in the first couple of cells, but can't seem to find a way to do this using just the start and stop values - does anyone know if this is possible?

Thank you!