It is a good approach as it is not as confronting as directly attacking the religion.
There are a number of similiarites that you can drop over time. I have an article about it at http://www.jwfacts.com/watchtower/similar-religions/mormon.php
A couple of old similarities are that Mormons believe they will rule with God on planets and the Watchtower used to teach that God lived in the Pleides.
"The constellation of the seven stars forming the Pleides appears to be the crowning center around which the known systems of the planets revolve even as our sun's planets obey the sun and travel in their respective orbits. It has been suggested, and with much weight, that one of the stars of that group is the dwelling-place of Jehovah and the place of the highest heavens; that it is the place to which the inspired writer referred when he said: "Hear thou from thy dwelling place, even from heaven" (2 Chron. 6:21); and that it is the place to which Job referred when under inspiration he wrote: "Canst thou bind the sweet influences of Pleiades, or loose the bands of Orion?"--Job 38:31.
Also http://www.jwfacts.com/watchtower/quotes/black-skin.php discusses the old view the Watchtower had regarding black people that is similiar to the old Mormon view of African Americans.
Both Joseph Smith and Russell were disillusioned Presbyterians and instead of joining another religion decided to start their own religions. This is very important as most JWs do not think enough at how illogical it is that some guy just started a religion and expect others to believe they alone represent God and Truth.