Fellenius method was the original (first) method.
So, even may be it is not the best method, from a teaching point of view, it is interesting.
Fellenius considers that the resultant force in vertical planes are paralell to the base (or you can consider it zero, as they do not appear in the calculations).
If you don't want to implent the method from scracth, you can just use the result from morgensteng-price after the first step when you have initialize normal and shear force on the vertical planes to zero.
So it should be very easy to provide the results from fellenius method (slide always provide fellenius results as it is used in bishop, or jambu as the starting FOS for FOR iterations.