i have my own ball and shoes, i go bowling like once a week. i've bowled a 205 before, but i'm able to control the ball much better at the lanes than on wii sports
Although I can see where you guys are having trouble with it, it is a hard thing to rotate your hand to the left or right as you are letting go of the ball
If i want right spin, i twist my hand right, if i want left spin, i twist my hand left.
The motion that comes most naturally to you must have a left spin tendancy. Find a spot to the right, aim it left one or two clicks, and take advantage.