How do I Argue Unreasonable Write Offs for Grossing Up Income for Child Support?

[momto3]

How do I make an arguement for unreasonable write offs to convince a judge to gross up my ex's income for child support payments and proportionate share of s.7 expenses, for example, he writes off 100% of his vehicle, writes off home office expenses when he has an office, pays 60% of his commission to his office for "expenses" with his share being only 50% of his gross income. He is a realtor and writes off $12k plus for meals (from reading Canlii it appears that judges don't really look at this as a valid write off where child support is concerned)