Union fees based on hours worked

I am researching an interesting issue we've recently come across.  We have a single location of ours that has unionized.  The issue we're running into is that the union has agreed to union dues for their members based on how many hours they have worked.  Oracle has recommended that we build a custom sqr to handle this and insert into one time deductions.  The other possibility is for us to use the special deduction calc process, although that would require customization of the PSPDEDTN cobol (doable, but who really wants to modify any more COBOL that we have to?).  The