yes, your DSC needs to be off. If it is still somewhat engaged, individual braking of the wheels will result, and the computer will try to point your car in the direction of your steering angle, which will instantly spoil your drift. With DSC on you can still do a little bit of a momentum drift as long as your entry speed is high enough. But you have no way of maintaining that drift with your throttle. Once the inertia is gone, your drift stops. But this is highly not recommended as the car becomes VERY unpredictable with double-corrections and shit. Best to off DSC completely.
Without a clutch pedal, you cannot do those "pump clutch to drastically and suddenly change your rear wheel speed" kind of drifts. But that only takes 1 method out of the book. The easiest to perform in a BMW M, is actually a power over. Coz the weight balance is very neutral, the degree of error an amatuer drifter can go into is a lot larger, before the car spins out. Momentum and weight transfer drifts, including braking drifts, can easily be done and is independent of clutch-induced drifts.
Once the drift is initiated, the rear diff work really very well in letting you maintain your slip angle. If you feel your slip angle or your drift tapering off halfway, yes, you cannot pump the clutch again to slip the rear wheels, boh pian. If your speed is still a bit high-ish, then try a bit of handbrake to replace the lack of a clutch. If your speed is not too high, you can pump in a bit more throttle. As far as possible, no need to use clutch to initiate or maintain a drift, coz you are using your own car, and it causes a lot of shock to the driveline, very sim tiah you know.
Because the M is thankfully still an NA car for now, amatuer drifters can still easily control the car. Unlike pro drifters who can skilfully keep the boost on with higher revs with their high speed drifts, I always have a problem with throttle because my stupid revs drop too much resulting in the turbos coming on and off, spoiling the balance. So this M package is really very good for drifting. You dont need a conventional manual tranny for this. Only gripe is that the conventional M steering wheel is a bit too fat for proper steering play. But still can la.