Currently, there is not. You can turn off processing altogether, but cannot choose which ones auto process. The only way around this is to continue to uncheck walkout and schedule appointment when posting.
@drcavola brings up a good point that I failed to consider. If you navigate here:
You will see the menu that @drcavola posted a screenshot of. If your settings are set to Automatically Process, then it will process insurance, walkouts, and appointment questions automatically. Within this dropdown menu, you can select Do Not Process, or Ask To Process. The Ask To Process option will be best for your office if you wish to deselect the walkout and appointment questions when posting. If your office is already using this option, then there is no way within SoftDent (right now) that only insurance will auto process without you having to deselect other items before proceeding.