Okay.
You probably could have purchased another UNO for the same price, and used that as an ISP programmer and second serial interface via software serial.
Another option is to have your sketch send ASCII commands via the serial monitor, and then once you're happy with what its doing switch it to binary commands and load the MIDI firmware to the 8u2.
I'd recommend taking the "risk". You'll learn some useful skills and get a native USB MIDI device out of the effort.