Don't do it. Under stress, the sympathetic nervous system will cause some degree of symmetrical muscle response, causing your support hand to pull the trigger the same as your strong hand. This will pull on the trigger guard and send shots flying erratically. Unless you've trained to such a high level that your body is completely immune to stress and the effects of fight or flight response. This would be the case for most top level competition shooters. However, when the paper targets start shooting back, bad technique will cause groups to open up, no matter how much training you have.