That would be a waste of a bonus.
You would only make $5. Sportingbet don't return the bonus to you. They only return the winnings from the bonus.
No, because it is not a free bet. For example, lets say you have $100 in your sportingbet account and want to put in another $100 for this bonus. You will get $150 put in you account. So you would then have $250. That extra $50 is not a free bet where you get just the winnings from ... it is just an extra $50 to add to the bankroll