Underpick in EWM

My customer has 'bulky' materials. If the customer fe asks 100 metres of a certain product, he would also be happy with 95 metres within order tolerances. The issue is how to automatically reduce the delivery quantity in my EWM ODO in order for the goods issue to pass without them first having to go in the delivery to reduce it. The picking is technically done with Z stuff in the RF framework, the RF transaction makes the tasks while the worker chooses the from bin and the HU he wants...

Technically we use function /SCWM/TO_CREATE_WH to create the picking tasks....