Hypothetical Tax Question

Let's suppose someone put off their tax return until a couple of days before the deadline(like the real 3-year deadline, not the April 15 deadline), and discovered they were missing some receipts for deductible expenses, but have the credit card statements so know for certain the amount. But businesses being what they are, getting copies of the receipts before the deadline ain't gonna happen(like you need to snail mail a written request and then it will take a couple of weeks). Is it kosher to file the deductions, know the return will get flagged, then produce the receipts upon demand from the IRS if/when they ask?

Hypothetical Tax Question