If the bitAsset is more fairly priced on an external exchange, buy on that exchange, and sell it on the internal exchange. That's an instant profit.
If the bitAsset is also at a premium on the external exchange, you could go long and short, and hopefully match these without somebody stepping in the way of either order. Then you could sell the long on the other exchange and exchange it for exposure to the underlying asset. That way you are hedged in BTS, and have sold bitAsset at a premium. As Chronos raises, your profit is not guaranteed, and depends on the premium reverting back at some point, so you have to be willing and able to hold (avoiding margin calls etc) to get this profit.
If the bitAsset does not trade on another exchange, you would have to short the bitAsset and separately sell BTS and buy the underlying asset on other exchanges. Again you have to hold until prices revert.
There are risks and costs in all these strategies. If we can minimise these risks and costs, and simplify the management of these strategies, then I believe we go a long way to improving the pegs going forward and avoiding these types of situations. It would also help gateways to offer narrower spreads. I've been addressing that issue in some other threads.