I would try it this way. The following code snippet must be executed every 10msec, invoked by a timer interrupt, for instance. The code uses one register set r0-7, so the original values from the main program must be saved and/or bank switching must be used:

mov r7,r6
mov r6,r5
mov r5,r4
mov r4,r3
mov r3,r2

mov a,p1
mov r2,a

cpl a
anl a,r7
anl a,r6
anl a,r5
anl a,r4
anl a,r3

mov r0,a
orl a,p2
mov r1,a
mov a,r0
anl a,p2
cpl a
anl a,r1

mov p2,a

I'm busy right now, will comment it later.

Kai