That’s why you need to be able to calculate the amount of braking torque it will produce and PWM the FETs between braking and freewheeling.
The question is whether freewheeling (all FETs disabled) will still cause overvoltage due to the body diodes? The more I look at the this diagram, the more I think the answer is yes. Even with all FETs disabled, current can flow from battery-, through a low side body diode, through the motor, through a high side body diode, and to battery+. So my dream is probably impossible 
There’s also the option to commutate the motor with d-axis current to waste energy without producing torque. But that probably needs current sense, and I want something that works even with the most basic hardware.