hi,
indeed, it is possible.

1) Connect RAM as external data memory controlled with /RD and /WR. Connect ROM as external program memory controlled with /PSEN as /OE. As well, connect /CS of RAM and ROM to GND. With this way you will be able to access RAM via MOVX commands inside 0x0000...0xFFFF address range and ROM via MOVC command within address range you_mcu_internal_flash+1...0xFFFF. As you see, there is limit of external program memory size equal to 64kb-internal_mcu_flash_size.
2) If you have two pins free then you may use them as /CS signals for RAM and ROM chips. With this way you will be able to use full address range for both chips via MOVX instructions (/RD for /OE of RAM and ROM; /WR to /WR of RAM; one free pin to /CS of RAM and another - to /CS of ROM. With it you select active chip with dedicated pin, execute MOVX, then deselect it.
In both cases you need to one more external chip for low address latch controlled with ALE.

Regards,
Oleg