Custom Sort of Duplicated row walues in Webi based on SAP BW Universe

This is regarding custom sorting of row value which are duplicated in Webi which is based on SAP BW Universe.

I have created Webi Report based on Characteristic structure. Using Alerter I provide some space for child node to notify it as child node below a parent node.

Please see a sample table below:

AAAA

onpeak

midpeak

offpeak

BBBB

onpeak

midpeak

offpeak.

If I enable Avoid duplicate row aggregation, i will be able to see duplicate rows for "onpeak" etc. Since Webi does a default sorting, I have to make a custom sort to replicate the structure followed. And in custom sort i dont see duplicated rows, and i see only one "onpeak". Accordingly if I try to sort using custom sort, then the result will be

AAAA

onpeak

onpeak

midpeak

midpeak

offpeak

offpeak

BBBB.

Please let me know if anyone has any solution for this.