There’s no built-in system for it, but I had some success experimenting with it a couple weeks ago here using the also-experimental angle_nocascade mode.
What kind of position sensor are you using? When I tried a 14-bit AS5048A, the jitter while holding position was so small that it doesn’t really seem necessary to disengage.
EDIT: Oops, failed to read the post title. In open loop, you can probably just set motor.voltage_limit = 0 if the target hasn’t been changed recently.