Aux input for MP3 player

I have been using a Scotsch? transmitter to connect a MP3 player to the stock stereo in my '06 TL. It works but drives me crazy as local stations start to cause interference. I always seem to be looking for empty stations.

Is there a simple way to add an auxiliary jack to allow direct connection? My wife's 2011 Nissan 370Z has one and it works great. Of course it needs an USB charger to keep the MP3 player charged.

I am not an electronics wizard and the car is now 9 years old so I don't plan to make a big upgrade in stereo equipment.

Any ideas?

Thanks,

Ranger