Update UD after SSRS dataset sent to reporting server

Hi,

I am stuck, help if someone can.

So I need to update ud after dataset submited for printing(the idea is to increase UD number by qty of labels being printed). So I built UBAQ and added BPM on GetList, created report with BAQ Report Designer, it worked it updated number under UD table:


But with report designer I can not pass silent parameters, so I recreated report by building custom data definition to be able to pass silent parameters to UBAQ. It worked, I am able to pass silent parameters, but now seems it does not work as an updatable BAQ anymore. How can I solve this if I need that update would be called only after BAQ result being sent to reporting server?
I am thinking about creating outer BPM on
image
But have no idea if this would work and in this stage parameters were sent in XML format and I dont know how to retrieve specific value from XML:


So can anyone help me to solve this puzzle?