Shadowbox-JS: pass Flash Vars thru custom field?

ok so im using the Shadowbox for an artist/musician’s portfolio site and furthermore the JWFlash Player for .mp3 files and i would like to display an image in the player while listening to said .mp3’s, which i can do from the plugin’s settings admin, but more specifically i would like to make that image unique to each .mp3 file. the site is set up where posts are nothing but a custom field containing thumbnail images, hidden until :hover’d, and a URL in the content that is applied to pre-made anchor in the index.php template and so clicking a post enables Shadowbox and the user sees the blowup/plays the .mp3 selected. im hoping that i can just post an image or URL in another custom field to be passed as a Flash Var for each .mp3 post.

does that make sense? is this possible? please let me know if i need to (or how) i can better explain this… thank you.