Hi,
Ivan, there are two ways I see:

1) Standard: Use external address latch chip (74574) and ALE connected to its /C pin. This way, the chip latches low byte of address and provides it to RTC so you may use DPL or R0/1 content as accesed address during MOVX.

2) If you have enough MCU pins then connect pins of P2 to the address lines of RTC. This way, you may select address either with DPH (in case of usage MOVX @DPTR) or just with P2 content (during MOVX @R0/1 - the content of these registers is not important: dummy usage).

As about /CS. This signal may be done:
- with AND gate (okay, Erik: with negative OR :) from /WR and /RD;
- or using another free MCU pin (not good idea);
- or in case you have not other external devices, connect it to GND (the worst idea!).

Regards,
Oleg