Anachronism

I have noticed that the wiring harnesses for adding an aftermarket head unit have RCA jacks for line in to the factory Bose amplifier. Is there any way to add this line in but keep the factory head unit? I am guessing it would require some sort of switch.

I have a 2003 Maxima with the factory bose in dash 6CD changer. I have not been able to find any aftermarket solutions for adding line in since most (all?) use the port for an external CD changer. I was using a cassette adapter that gave (barely) acceptable sound quality but the cassette deck died on me (keeps giving 'tape error' message, I have tried more than 1 cassette adapter). I am now using an FM transmitter but I am not very happy with it.

I do have an iPod charger with line out that I would use. 90% of my listening comes from my iPod, I am almost willing to bypass the factory radio altogether (but not quite )

I actually have an aftermarket head unit with line in but I would rather keep the factory look. Also after buying the mounting kit and adapters it looks like there is some expense to installing it.

EDIT - I would be willing to use the line in for the factory 6 CD changer or cassette deck (even if I couldn't use them anymore) if that where an option but while I am fairly handy with wiring, disassembling the radio and soldering to the board may be beyond my abilities.