All of our babies start on live left in their enclosure. After a few good meals I will start trying to get them feeding from tongs. Once they are used to taking food from tongs I start feeding fresh killed. Once they begin taking fresh killed I start with f/t.
Make sure you are feeding at night for the best chance of success. Use a hair dryer to get the head of the f/t mouse up to 100-108f. It seems they take f/t more readily when they are nice and warm.
Good luck.