One possible, though awkward workaround if you don't have Jeff's chrome plug-in is to ask if that other person has a relatively uncommon surname in his tree and then just do a surname filter search with that surname and your match will likely show up in your search results. If the surname is really uncommon, he or she may be the only one to show up if you're lucky. Of course, you could also do a search using the surname of the suspected common ancestor and if you're lucky, not only will you come up with your match's name but also other people from your match list who may have connections to the same person or family.