EDIT: I just noticed your question asks for App Engine specific solution. This solution only applies if you have 100% control over the Linux server running your code, so this does not work on App Engine (or I have no idea does it nowadays have capability of tunnel building). In any case I recommend you to move your code to a virtual server from the app engine to have more control over your stack, as you might hit App Engine limitations quite fast if polling bitcoind for transactions.

Build a TCP/IP tunnel through SSH from the computer running your code to to the server running bitcoind.

One easy way to build such a tunnel which restarts itself on disconnect is AutoSSH.

Here is one AutoSSH example script:

http://www.ubuntugeek.com/automatically-restart-ssh-sessions-and-tunnels-using-autossh.html

EDIT: I just noticed your question asks for App Engine specific solution. This solution only applies if you have 100% control over the Linux server running your code, so this does not work on App Engine (or I have no idea does it nowadays have capability of tunnel building). In any case I recommend you to move your code to a virtual server from the app engine to have more control over your stack, as you might hit App Engine limitations quite fast if polling bitcoind for transactions.

Build a TCP/IP tunnel through SSH from the computer running your code to the server running bitcoind.

One easy way to build such a tunnel which restarts itself on disconnect is AutoSSH.

Here is one AutoSSH example script:

http://www.ubuntugeek.com/automatically-restart-ssh-sessions-and-tunnels-using-autossh.html