TreeSeek has just released a Relationship Calculator (beta). It is a web-based tool that will allow you to enter two FamilySearch IDs and calculate their relationship to each other. The website says if the person is living it will calculate the closest deceased person's relationship. I wasn't successful in having it calculate my relationship to my direct line ancestors, but it did work great when dealing with all deceased individual's relationship.
To access the Relationship Calculator go here - http://treeseek.com/tools/related/