[Moneyline]

I would rather call on the flop. You are basically looking for a 2 or a 7. An ace or a 4 or two running spades might also be good cards for you (particularly the A). Nevertheless, I think you aren't going to win 1/2 the pot without one of these specific cards, so I would rather call. If you are fairly certain this player will fold a missed low draw on the river, I don't think you need to set that bluff up now. IMO just bluffing on the river should be sufficient.

Edit: I think it's also worth noting that if you make you hand you have a good chance to scoop. Just because you put SB on a low doesn't necessarily mean that is what SB holds. In addition, one of your outs (the 2) will probably scoop for you since it ruins the most likely low draw... this is also why an A is probably good for you too (but not as good).