Main:
  [...]
  call Function1
  [...]
  call Function2
  [...]

;the real ("Original") functions are here:
O_Function1:
  [... some code then ret ...]

O_Function2:
  [... some code then ret ...]

;JumpTable begins here
  ORG  SomeSuitableFixedAddress
Function1:  jmp   O_Function1
Function2:  jmp   O_Function2
  [etc...]