Rather than having people commute in on "Paperwork Only" days, allow employees who do not already telecommute to do so on days where only clerical or administrative tasks (such as filling out paperwork) need to be completed.
Let's assume that commuting costs workers roughly 1 hour of time, $10 in gas per day (3 gallons), plus at least $10 per day in miscellaneous expenses (lunch, soda, etc.). Let's also assume that you need just 1 admin/clerical days per month on average. The average hourly rate for Federal employees is $35/hour (all employees averaged)
That nets a savings of more than $50 per day worked at home vs. commuting just for paperwork.
With more than 2 million workers, just one such day per month could save more than $1.2 Billion in lost time and additional expenses per year.