SVN is pretty much not able to do this (easily,) by design. What you really want is the ability to 'offline commit', meaning you can just make commits that stay in your repository and then you push them publically when you want.
There is a tool, SVK, which allows you to do this in the context of SVN (specifically, it is an SVN client with offline commit and other stuff.) Note: it will *not* make it easier to commit to two different SVN servers, it will merely allow you to pool commits locally until you decide to push them to the actual, user-viewable server.
I however, recommend jumping ship from SVN and using a distributed version control system like Mercurial or Git. They allow you to work exactly how you want and offer much more.
