Hmm…I get that you don’t want custom programming, but I think this would be way easier if you did allow at least the setting of a variable by a c# expression using the Set Argument/Variable widget.
and I haven’t been fully caffeinated this morning yet either, so bear with me, but I also assume you know how to create local variables within the BPM? That would give you a place to store your data and then parse out to set your field