ASH,
You can shoot any release using backtension, index included. The best thing to do when learning proper backtension is to do it on a bale 5 feet in front of you with your eyes closed for quite a while. You really have to committ to staying off of a targetwhile learning, with that said 95% of people will not make it one day without trying it out on a spot and eventually give backtension up because the results were worse than punching a trigger on command. If you want, let me know and I can help you out with a step by step approach that you can do inside at home to get you started the right way. Remember people will tell you you have to shoot backtension "this way" but really there are 3 different ways to properly shoot backtension, you just have to try them out and decide which one works best for you,

Billy