Further to my post about creating properties files when I had text files in unicode, we decided that the best thing was to have a web application to do the conversion. You can then just paste in whatever text you want to encode and it tells you what the java escaped text string(s) should be.
And, we decided we might as well make it publicly available. So here it is.
Let us know if you find any bugs or if you can think of a better way to do it