Kevin,
in general this can be done if EA is 1 and
the ADC code is executed from internal Rom

But be very carefully that you don't do any
external access via MOVX or MOVC because this
would alter P0 and P2 contents.

Like Eric said in another thread:
Errors in such designs are very hard to debug.
Note : you will need pullups on P0 in this case.

Thomas