What model year is your EX head unit?

The 98-00 EX head unit has a plug to accept a tape deck or a trunk mount CD player from Honda.

You could either

A: See if the newer Honda MP3 player would plug in to the unit.

or

B: install a trunk mount 3rd party CD player-changer.

For example: you could install a Kenwood changer in the trunk and use the Kenwood KCA-R70FM (R71FM) controller to controll the unit. And via the R70FM you could run RCA's into a 3rd party adapter like a blitz-safe unit giving you clear audio just like stock.

A bit complicated but in the end you could add anywhere from 6-24disc in the trunk or armrest.

The nice thing about the KCA-R70FM is that it would also allow you to add a Sirius or XM tuner in the trunk as well should you desire.

I had one in my Accord running Sirius but it works with a changer as well.