GPO to configure L2TP VPN

So looking at finally getting rid of my Cisco VPN and replacing with Meraki (also Cisco, now). Their client VPN is strictly L2TP and that part works fine.

What I'm looking to do is deploy the configuration globally using Group Policy and this is where I run into a problem. I can configure the VPN portion just fine but there's no where to enter the pre-shared key! Manually configure and it's right in the advanced settings, but nothing in the GPO settings.

I found this:

http://social.technet.microsoft.com/Forums/windowsserver/en-US/e92cafd0-6e0a-4757-b3c8-9f5bfd108fb8/deploy-ipsec-vpn-with-preshared-key-via-gp

And tried it but no joy.

Has anyone actually done this kind of thing? Another one of those baffling problems that GPO has!