If spillover was a function on your handheld, then it should already show as an auxiliary function in iAqualink.
You can see Aux functions on the "Devices" page of the app (select at the bottom right of the app), or you can go to the Web browser function that is enabled at the top right of the app (or directly from your laptop browser) and see the Aux buttons after selecting "Other Devices" at the far right of the Home screen on the browser.
To edit spillover activity in your daily schedules, go to the Web browser, and from the Home screen, hit Menu->Schedule.