I've read many news stories recently complaining about how much it costs the government to stockpile dollar coins that aren't being used. If you want to get the coins into circulation and out of the warehouses, get the money out to military commisaries. Substituting paper money with dollar coins will be easier on military bases, as the Forces are used to taking orders, and trying out new things with no questions asked. From there, it will trickle it's way into general use, as service members use the coins offbase at various facilities.
This will eliminate the cost of storing and securing unused dollar coins, and when they replace paper bills, the public will already be more familiar with them.