Mpu 6050 Accelerometer Calibration

Hi,
2 questions:
1- Mpu-6050 used with Embedded Motion Apps allows you to set accelerometer bias manually by calling set_accel_bias function. Is there any way to set cross axes sensitivities as well? I have come around function set_accel_calibration, which allows you to pass a calibration matrix but the specification says it only allows 1 or -1's to be passed.
2- Is it possible to give acceleration values from an external accelerometer to the DMP so that these values will be used to find motion solution ( such as quaternions)?
Thanks.