I play wrestle with Russel and that usually gets him laying on his back, if you just tickle his belly, I also am teaching him to play dead, you hold him on his back for a second and then treat, you gradually increase the time that he holds still on his back and treat, he will realize the longer he stays still the more likely it is for him to get a treat, eventually you can open your hand and he still stay still on his back till you give him a treat. This may help because then hes used to laying on his back and thinks it will get him a treat. JUst make sure when you start out that you dont scare him when you hold him with his back against your hand. You a very gentle voice and slow movements.
Thanks Gals! She has almost rolled over on her own several times, and it is usually when she is in her happy hut or when she is being playful on the couch. I will work with her on it, but will not force it.