I don't know of a way. I believe the percentage is calculated within the charting JS, so you're not going to achieve anything within the search... and I don't see any setting to configure the rounding behaviour. The browser locale seems to be passed to the percentage formatting code, but I don't see how that would have a lot of sway over the number of decimal points. Additionally, changing the locale for this would probably cause more issues elsewhere than would be solved here.
You should ask this as a new question. Not only will you get the attention a new question deserves and not pollute two-year-old other questions with varying potentially version-specific info, but also make it easier for others to find what they need.
Off the top of my head I don't think the built-in pie charts have an option to move the labels to the inside of the pie, but you're always free to build a custom visualization and publish that as an app on splunkbase 🙂