honestly in my opinion (and this is purely my opinion), if something like pressing 8,9,0 simultaniously is against the TOS, is more a question what is ingame bound to 8,9,0 than how its achieved.
But this is only my interpretation, and of course the 'save'-path for everyone would be to simply don't use such 'simultanious' keys, but this doesn't mean, that it is allways against the TOS (imo)...

..maybe to get an end to this discussion, it would be of use, when you tell us, what exactly you want to bind to 8,9,0 and what should happen, when you press the '7' (which sends 8,9,0).

..well and to answer your question jefflo, something like you described, could be done in HKN, simply by the follwoing script.
(which as debated may be problematic, so I would use it only on your own risk)
Code:
<Hotkey 7>
  <SendFocusWin> 
      <Key 8>
      <key 9> 
       <key 0>
ok, and to give another example how to do this with being in the '1 key press per 1 action', you could use <toggle> for this, which would result in you needing to push '7' 3 times:
Code:
<Hotkey 7>
   <Toggle>
        <SendFocusWin> 
              <Key 8>
   <Toggle>
        <SendFocusWin> 
              <Key 9>
   <Toggle>
        <SendFocusWin> 
              <Key 0>