Allow the user to set a price in BTC (either a free form field or drop down menu) at which the miner starts. For example - set a BTC of 5600, the miner will check the price every minute or so, and when the price is at or above the desired value then mining starts. If the price dips below, the miner turns off.
An additional feature for a time based over ride would be nice as well. For example, mine if the price is over X but not between 1200 and 2000 hours local time.