Audio from a Microphone through iMic for YouTube

Hullo,
in order to publish videos on YouTube I follow a workflow consisting of recording by Quicktime, convertining to iMovie and then upload to YouTube from there.
I would like to take advantage of a Microphone in order to be able to sit farther away and so I also purchased a Griffin iMic. When I put everything together I had a humming audio on the left channel and just humming on the right.
Without having to acquire a Mixer, is there some way to replicate the left channel on the right in order to have a double mono and/or to load an audio on a channel and another (for example a song from iTunes) on the other?
Can I do it by QT or iMovie or I need to get some other software (possibily free) that anyway fits into the aforementioned workflow?

Thanks,
Fabrizio Bartolomucci