Triggerbot is a Windows app that can help you send song triggers accurately to IMVU. It's currently a work in progress. If you're interested, you can download and install it and try it out for yourself.
Additionally, you can easily create new CHKN files from MP3 files on your local computer. This feature is still in development and getting better every week.
Download Triggerbot Setup 0.9.0 (beta): triggerbot-setup.0.9.0.exe (15 MB). Once installed, you'll be prompted to upgrade when an update is available.
Instructional Video. View in fullscreen mode at 1080p HD for the most realistic experience.