If you can do it on the forehand you can do it on the backhand. The ball doesnt care which side you hit topspin from. It only cares how the racquet meets the ball. If you're not hitting topspin, then you got to get the racquet lower then the ball before going up through it. Look at your forehand swing in slow motion and find out how it gets lower then the ball then comes up to meet it, then duplicate th swing path for your backhand.
It is easier to get your racquet below the ball on the forehand. On the backhand you almost have to feel "weird" getting lower, that you think you're not going to hit it right - then trust it and swing up with a level racquet and perpendicular racquet face to the court.
The first thing you should do is practice over and over again on slow balls, then increase the pace - really loop it. You will suddenly see you can do it but you need to learn to do it under pressure.
If you have a good penetrating slice I would hit that as well. If you want to just stick with that - nothing wrong with that idea. Just learn how to mix up the spin and speed and hieght of the ball. You will have to be excellent with your placement hitting the slice all the time.
Former USPTA Teaching Professional
Volkl Tour 10 V-Engine Mid/Luxilon Big Banger