The GL1 is a DV camcorder. You can capture live video + audio combined but it's not possible to capture just audio by itself. This is the nature of DV capturing, and Final Cut needs to have a combined audio & video stream over FireWire for capturing. So, you can't use this for VoiceOver.
A workaround would be to capture live from the camcorder for your v/o purposes, (you will be capturing both video + audio). Then in FCE unlink the audio tracks from the video track and delete the blank video track. But I wouldn't bother doing it that way because it's a hassle, and the mic in the GL1 isn't all that great.
Recommendation - get a decent mic and plug it into your Mac for voiceover recordings. You can use any dynamic XLR mic with an XLR female to 3.5mm male stereo adapter. You can pick up a Shure SM-58 for $99 new, $50-80 used.