Got the same problem here, and after some explorations, you can do this in javascript :
Microsoft.Translator.Widget.domTranslator.showHighlight = false;
Microsoft.Translator.Widget.domTranslator.showTooltips = false;
But this must be done after translation, in my case I use Web Widget Customization API, so i can hide tooltips in the onComplete callback of Translate function.
Beware, it's not documented, so I don't know how long this will work. But it's the only way I found.