Absolutely illegal

This has nothing to do with IRS audit or not.

Your own rental payment is like your car payment. Or your payment for a diamond. It is consumption.

Writing check directly or not does not change this fact.

The way to offset your rental income is to count all your cost relating to the rental income. In case you don't have a mortgage on it any more and your total cost is well below your rental income, you may want to consider an equity loan or HELOC to get cash out. That way your cost will be up, and you can use the money for other investment opportunity.