as far as i know there is no place for anything to plug in-line with the antenna, if that is the device you are talking about. The antenna connector is secured to the inner dashboard, and plugs into the radio when the unit is slid into the slot. It might be possible to fit the cables and whatever else is needed into the back of the radio if you were to un clip the antenna lead and let it back down into the dash area somewhere, keep in mid that the car uses a VW style antenna connector, not the standard GM one!
Could you provide us a link to the unit you are talking about for a possilbly more complete answer?
2002 Nissan Maxima SE - 15.143 at 91.74mph - Short Ram Intake - 2* Timing Advance- Tein Coilovers - Front Strut Brace
00-01 SE Tails - Smoked side markers - Painted and Cleared Headlights - Weathertech rainguards - Tinted to 27% - CF Gauge Trim
Stereo: Eclipse CD8445 - Kenwood KAC7201 - Kenwood KAC-729s - Cadence Components - 2x MB Quart Reference 12s
2000 Bonneville SE - Retired