Automatic folder selection

I'm using three tasks for converting SW drawings to DXF, PDF & eDrw's, which automatically launch during an "Approve" transition, which works perfectly.  What I would like to do, is to save these viewing files to a new folder, based on the assigned ECO number (which is a variable (t_number) automatically assigned to the ECO document via the serial number generator.  Assuming I'll be using the Advanced Scripting Options of the Convert Task, how can I get that ECO number variable (t_number) into the Primary Output Path?

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