ORG   0Bh
   lcall RealISR


   ORG   somewhere else
RealISR:
... the compiled ISR code ...
   reti

Give them some credit (Though I have seen compilers do worse)


something like:
   ORG   0Bh
   setb  p0.1  ;or whatever
   reti

would have to be in its own ASM module