But that still leaves the original problem: how do you know what address to use??
You can't do it using 'C' labels.

ISR:

RETURN:       
MOV SP,#9     ;maybe stack is anything first you load 9 on it
POP 7         ;with 2 pop you provide changing return addr
POP 7         
MOV R7,#01H   ;change upper address in pc -- But to what??
PUSH 7
MOV R7,#00H   ;change lower address in pc -- But to what??
PUSH 7
RETI