There are adapter units that plug into the back of the factory radio 12 pin connector (if your radio has one). These adapters supposedly do not interfere with the function of the radio or single or six disk changer. There may be other adapter out there but these are the one's I've seen others use in their Toyotas.
PIE Toy 03 Aux
http://www.logjamelectronics.com/pietoy03aux.html
USA Spec has one for the iPod, they used to have one with RCA connectors as well.
http://usaspec.com/product.php?ProductID=17
Another workaround if you don't want to run wires or pull apart a dash is to use an FM transmitter, its clunky but works. I've seen people use the Macally PodFM Transmitter,
, with a GPS unit to get audio through their Corolla's speakers.
Also check Chrutchfield,
http://www.crutchfield.com/m_770/iPo...ers.html?tp=15, as they may have additional auxiliary adapters that may fit the Corolla.