Constant torque mode is the same as constant current control. The new Pro-160 has direct motor current sensing and uses this to implement a fully adjustable current limit. The software to provide a full torque control mode is being developed.
The 4QD-200 & 300 have an adjustable current limit which can be used to limit the torque from the motor.
Remember that the standard current limit is there solely to protect the MOSFETs from transient over-currents which could be destructive. If you run on the standard current limit for too long, then the controller will simply overheat and melt – quite literally, it is indeed possible to melt the solder on the MOSFET leads before the controller fails! So you may need to reduce the current limit quite significantly. The exact allowable current will of course depend on your heatsinking, the motor, and the controller you use.