Rather than an Ostler-Smith attachment, why not just use an average of his annual income? If you get his W-2 for last year and divide it by 12, it will take into account the overtime he got paid over the course of last year.
If the court makes an order for the Smith Osler, you can ordinarily attach it to a wage assignment. There is a table which is generally attached to the dissomaster. If the court is not allowing this to be paid via wage assignment, you may wish to retain an attorney to argue this matter appropriately. Further your son's father is required to provide you with his checks so that you may calculate the Smith Osler based on the bonus or overtime table. If he fails to do so, you may be able to file a contempt proceeding against him.
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