Hi Gavin,
Set strategy to bet on your selection and then use "After bet rules->Hedge" and set it to execute when price goes up/down by X ticks.
Then at strategy "Edit" form set maximum number of bets per runner/market to higher value than 1.
Make sure you test this in simulation mode first, if you set it incorrectly then you could end up with large number of bets placed at the same time.