EACH TIME a spell is cast? No matter what spell? I don't get what you mean. However, if its about a single spell, and its regardless to the caster, just use a global variable which keeps in mind how many times the spell was cast (initial value should be 0). And everytime the unit casts the ability, first increment the variable and then have that action look like this:
Unit - Order Stepper to Move To ((Position of Caster) offset by (55.00*global variable) towards 0.00 degrees)
