I think you can do it using the statistical "summation" function and row functions. Here's an example for a 4-point moving average:

If(Row() < 4, Empty(), Summation(i = Row() - 3, Row(), :Column 1[i,Empty()]) / 4)

I used the "If" function to avoid errors when ( Row()-3 ) is less than 1. I'd be interested to see if someone else has a simpler way to do this.