**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][1].

Here is one AutoSSH example script:

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


  [1]: http://www.harding.motd.ca/autossh/