BCS Task for distribution based on sales

Hello Gurus,

We have added additional characteristic to BCS model -"line of business".

The target was to analyze our P&L with that segment.

Every item in BCS is presented with this characteristic that may get the values- '#', '1', '2'.

I am looking for a way to create a task that spreads the value '#' between the existing lines based on the proportions of periodic posting with '1' versus '2'.

For example account 12000 is uploaded from sap with 3 lines:

lob 1= $60, lob 2=$30, lob#=$9.

The task has to spread $9 from # to the others, and final result after should be lob1=$66, lob2=$33.

I thought that custom task might help but didn't find a way to enter a code there.

Any idea ?

Amos