This is going to sound weird, but chalk. Just regular white chalk from a chalkboard. Use it to colour over the grease stain, let it sit. If it's a big stain, apply a few times. Then kind of brush off the excess with your hand and chuck it in the wash as usual. The chalk draws out the grease, and I've done this successfully before with clothes that have been through the wash as well. Just keep applying until the stain is gone.

You'll see it too. The chalk around the stain will stay white but the chalk on the stain will change colour because it's absorbing the grease.