You can use a fourth shift register for full control over the 9 fields and their displays. The 3 displays use 21 segment outputs, so that 11 outputs are left for turning on/off up to 11 fields.
Then the displays should have common anode, which must be driven by a high side switch, e.g. 1 pnp transistor + resistors for each field. Circuit details depend on the supply voltage and segment currents of the displays.