Together with "What would be the benefit of doing so, on a relatively slow 8-bit system?" (backed up with "what is the fundamental reason for using buffering for graphics?")

I understand that you might not be in the position to "return" with this sort of questions to your mentor, just be aware of that his request is in this case unreasonable, so you might perhaps come up also with an unreasonable solution, like storing the buffer to FLASH (which is a workable, but fundamentally broken concept for both speed and quick FLASH wearout).

Please note that the 1kB RAM of P89V51RD2 is a slight marketing trick from Philips/NXP: it in fact contains only 768 bytes of "extended" "internal-external" MOVX-accessed RAM; the rest 256 bytes is the "standard" RAM all 8052-derivatives have (including stack, registers, bit-addressable area), to be set aside for more precious tasks than a "bulk" buffer storage.

JW


PS. Some GLCDs contain much more memory than they can display, providing a register to point to address where to display from - this can be used for buffering - check out your model.