The synthetic long straddle is equivalent to the natural. Three comms involved. Say you're long XYZ from a cost-basis of 100 and the shares are trading at 140 in December. You want to book your gains but would prefer to defer the taxes. You short two of the Jan 150 calls at 7.00. You're synthetically short the 150 straddle, one contract, from 24.00 premium. There are reasons (above) to trade the synthetic, but understand that they are fungible. There is nothing to exploit there.