Babel transform, get value of parent scope constant

Assume I have such Javascript code

import someFunc from 'somewhere';
const prefix = 'Planet';
someFunc(prefix + 'Earth');

If I use babeljs in my project I can write simple transform plugin

export default function({types: t}) {
  return {
    visitor: {
      CallExpression: {
        enter(path, {opts, file}) {
          if (path.node.callee.name !== 'someFunc') {
            return;
          }
          <...>
        }
      }
    }
  }
}

How can I take 'prefix' variable value inside plugin or evaluate whole BinaryExpression expression to replace it with result string to get this?

import someFunc from 'somewhere';
someFunc('PlanetEarth');