Note: First update the router to a recent build. Any build released after February 12, 2012 builds will suffice.
FlashRouters offers plug and play DD-WRT Routers preconfigured Private Internet Access Routers for this setup.
Step 1: Go to the Administration Tab and click on the Commands Tab.
Step 2: Copy & Paste the following within the Command field box:
curl --insecure --silent [ https://api.flashroutersapp.com/api/v1.0/ddwrt/group/default/provider/PIA/install] | sh
Step 3: Select Run Command and wait a couple seconds.
Step 4: Select the Status Tab and click on My Page
Step 5: Set the following: