Thanks for the help, I'll give that a try. I would love to see the finish prompt removed with an option just like all the others (BEST options page I've ever seen BTW). It honestly serves no purpose, especially with the done sound. The fewer mandatory clicks there are, the better.
EDIT: Your suggested command was 90% of the way there. I ended up making the following changes and it works perfectly, thanks a lot!
"C:\Program Files (x86)\ImgBurn\ImgBurn.exe" /MODE BUILD /BUILDMODE IMAGEFILE /SOURCE %1 /DEST %1.iso /START /CLOSESUCCESS