After a bit of sweat, here's the solution -- I hope this saves another soul a few moments of their life.  In the end, it's a matter of getting and reusing a few variables.  Prerequisites I won't cover are that you have a Facebook app created and ready to go, and a Location page to which you want to add the app canvas.  The variables we'll touch are :

  1.  Facebook App ID
  2.  Facebook App Access Token w/manage_pages permission
  3.  Parent Page ID
  4.  Parent Page Access Token
  5.  Location Page ID
  6.  Location Page Access Token

Getting the Deed Done

  • First, go to the graph explorer at http://developers.facebook.com/tools/explorer/
  • Select your application in the drop-down at top right
  • Click on Get Access Token
  • In the dialog that appears, go to Extended Permissions, and ensure that "manage_pages" is checked
  • Click Get Access Token in the Dialog
  • The token will auto-populate in the Access Token box within the Graph Explorer
  • Change the Graph API textfield to:  /me/accounts and request via GET
  • The JSON list will return the pages you have rights to administer.  If the parent page (parent to the location you want to add a canvas to) is not listed, you don't have the necessary rights -- get them first, then continue. ote the access token and id of the parent page.
  • Copy and paste the parent page access token into the Access Token textfield at the top of the explorer
  • Copy and paste the parent page id into the request box, changing it to PARENT_PAGE_ID/locations
  • Submit via GET.  That'll list all locations.  You should see your location listed.  If you have a ton of them and the list is a pain to read, you can lift it from the URL while you're inside your Location's admin settings panel.  Copy your location id
  • hange the request box to:  LOCATION_ID?fields=access_token
  • Submit via GET
  • The response will contain the location id (repeated) and the location access token  
  • Copy and paste the location access token into the Access Token textfield
  • Change the graph URL to LOCATION_ID/tabs and the method to POST
  • dd a variable `app_id` whose value is the app id whose canvas you want to add (you get the app id from the developer apps panel)
  • Submit (via POST) -- the response will be 'true'

Worked for me, repeated twice, what a PITA.  Good luck.