PearsonArtPhoto answers why it isn't done - generally NASA's very conservative approach to spacecraft safety, and hurdles it would set to get it implemented.
But assuming a miraculous change in NASA management and organizational culture, it would be fairly simple.
The engines have enough thrust to provide 4g of acceleration and are angled outwards and ...
There is no plan to do this, nor has there ever been an extensively studied plan. In theory it could be done, but NASA would want to certify it, and it is just better to spend more effort to make sure the primary mode works every time.