Oyster pay as you go on South West Trains?

If you believed the leaflets and posters at South West Trains stations you'd be led to believe that you could use Oyster pay as you go on their trains now. You can if you want to pay for your journey entirely on pay as you go. What about those of us who have monthly travelcards and want to travel out of zone on SWT services by using pay as you go to "top up" our journey as we do on the tube? We have to get an "Oyster Extension Permit" for each out of zone journey.

I frequently travel from Islington where I live to South West London where I grew up. I can get an extension at Finsbury Park, Highbury and Islington or Angel. However, when I want to return from Hampton or Teddington I can't get another permit because SWT ticket machines don't sell them. The SWT stations I use are also far away from newsagents that sell Oyster and those that are "close" are closed after 6pm meaning I can't get a permit for evening journeys.

This means I'm stuck either having to queue for 20-30 minutes at Waterloo to get a paper return, risk fare evasion or buy a travelcard to avoid queuing and pay for parts of my journey twice. You couldn't make it up.

Boris Watch has written about this absurdity. Reading the comments shows how little SWT wanted to accept PAYG and how unwieldy the implementation has been. Diamond Geezer found the same. I really don't understand why something that could and should be so simple has to be so complicated. A little use of governmental iron fist would have been useful here, rather than leaving it to our disinterested mayor to negotiate.