Because there is no such thing as a DC nonresident return.

There is a D-40B SUB Nonresident Request for Refund form. That's what you need.

Taxpayer needs to get employer to stop withholding DC tax. Bonus points if he gets them to withhold VA.

DC, Maryland and Virginia have an agreement not to tax employees based on their work location but in their resident state.  Employers should withhold state income tax based on the resident state.  

In your case where a taxpayer works in DC and lives in VA, he has no filing obligation to DC.  He is fully taxable in Virginia.  The only filing obligation he MAY have is if he has DC withholding and needs to file a claim for refund.