Photoshops "Match Colour" tool will help you match the grade of any layer to another layer. It doesn't do all the work for you, but it can often get you 90% of the way there.

Make sure you never rely on a single grading technique in your work. You want to have a small arsenal of techniques to try when you're working as each image is unique and will respond differently to grading techniques. This particular technique is really great for the early phases of grading when we're not so concerned with degrading the image as we can replace it later once we're certain we're going to use it.