Toyota AUX plug w/ aftermarket radio?

[eight_heads]

i've got an '07 liftback w/convenience pkg. here in the states so i have the factory AUX input for an ipod or other type of device... i loved having that feature right were it is at.... well, i just changed out my stock stereo to a nice premier pioneer head unit i had in my other car... i want to be able to use the stock aux jack with my aftermarket radio... is there any kind of adapter to go from the aux plug in the dash to say an rca plug? i know how to go the other way and add aux input to the stock radio, but i want to be able to just use the stock plug outlet w. my aftermarket radio that already has rca inputs... anyone?