Since summary fields also can summarize a related set, you should be able to simply go to an appropriate JoinTable record and use this script step
Set Field [ JoinTable::summarizedValue ; Audit::sSomeTotal ]
Should that for some reason not work for some reason (e.g. because I did not understand your structure), read the summary value into a variable (Set Variable), go to the appropriate JoinTable record and write the value (Set Field).
PS: No offence, but this is painful to the eyes:
Please do not use an apostrophe to form a plural (<shudder> )