Just a simple delay should work fine for you. I don't use SoundForge or Vegas so I can't tell you specifics, but I would do it by either:
1) route your delay as a send effect through your virtual mixer and just boost the delay send for the last syllable. This would be a non-destructive way of editing and I don't know if it applys to SoundForge.
2) you can splice or isolate your the last syllable of your sound file and just apply a delay effect to that which would be a destructive way to edit but might be just fine for what you want to accomplish.
Hopefully someone with SoundForge knowlege will jump on here to give you some specifics.