My language is served by several "off-line" machine translation tools, but they do not offer Java plugins.
If you have one of these, you can use it in the same way as an "on-line" MT service without a plugin, and more importantly, without breaching your duty of confidentiality.
1. Translate the source document with the off-line MT tool, and save the translation. To the best of my knowledge, those tools can save the translation as either .csv or .txt or .tmx. If it does not support .tmx, CT can import a TM in Excel or text format (see Memory > Import).
2. Open that TM (as read-only), right-click on the panel, and select "Keep out of auto-assembling."
Now, the TM is automatically looked up without its translation being automatically inserted into the target segment.