Question about Statistical Forecast

Hi,

We are trying to configure Statistical Forecast and the challenge is the planning level:

Our input KF is called Sales History and has a base planning level as:
PE/PRD/SOG/SOF/SGP/DC/ST   (Period/Product/S.Org/S.Off/S.Gp/Dist.Channel/Sold-To level)

however we want our forecast to be run at a more aggregate level as:
PE/PRD/SOG/SOF    (Period/Product/S.Org/S.Off),

i.e. without 3 levels SGP/DC/ST (S.Gp/Dist.Channel/Sold-To level)

My questions are:

1)  How can we forecast at an aggregate level without using too many helper KFs?
2)  Given that input KF and output KF for statistical forecast have to be at the same the aggregated planning level, how can we disaggregate forecast result back to the detail level?

Thank you.

Yee Ann