Try the McCartney method - when he wrote "Yesterday" he couldn't believe he hadn't heard it somewhere else - he ran around asking if his mates had ever heard it before.

I like Ed's idea. Write it and post it.
Writers often learn their trade writing to other people's tunes as an exercise.
Burton Cummings of the Guess Who would use a metronome to set the beat then play some chords - hard not to get something original that way. Set the beat with BB drums and mute everything else - then start to play chords - hard not to get something original that way.

You've got an idea - just write the song - worry about the rest later.
Cheers

Ian
My "Original Tunes" Site
My gene pool needs more chlorine.