Your ION has a remote trigger connector on the back of the console that can be used to trigger cues, submasters or macros. If you wire up a simple switch, you could trigger a bump button to fade up/out a sub with your houselight channels.
Check out the Eos Family Show Control User Guide ("Analog Inputs" starting on page 23) for information on programming the console. It is at http://www.etcconnect.com/WorkArea/DownloadAsset.aspx?id=10737461372
Information on wiring the connector is in the ION user manual.
In reply to tdrga: