Forward looking moving average or moving sum

Does anyone know how to calculated a forward looking moving sum or average (for time series data)?  Is there an operator that does this so that the look forward length is a variable than can be optimized?  From what I can tell, this is not possible.  This is very useful for averaging out noisy time series data.

NB -- this is different than calculating a moving average and then taking the difference of that moving average for each example.

Thanks,

Rob