Actually it would be pretty easy.
You'll need an FM modulator, an on/off switch and a 1/8" mini jack to RCA adapter. Hook the RF modulator in to the antenna line behind the radio and put the on/off switch in-line on the power wire to turn the modultor on and off. Plug the RCA jacks from the mini jack adapter in to the modulator. Now you can hook any device that has a headphone jack output on it up to you radio.
If you need a USB connection you will need to get hold of an older Sony Rf modulator with Uni-link changer control and an XA-300 Aux, input adapter. This will let you add a Sony changer with two more aux. inputs, one with an adjustable headphone output, and also a USB input.
The first method with be cheaper and easier though.