Alternative programming methods for programming a Mega

Hello- I'm trying to program an Arduino Mega r3 that will be 6 meters / 20 feet of cable length away. The Mega is also in a tight space, and I'm hoping not use a USB cable to program the Mega. I have tried using the FTDI Basic Breakout from Sparkfun, but that did not work with the Mega. I was able to successfully program a Diecimila with the Sparkfun FTDI Basic Breakout.

I've also seen, but have not tried using the USB Serial Light adapter that uses the ATmega8U2, which is similar to the ATmega16U2 found on the Mega. Could this adapter solve this problem with programming the Mega?

Thank you in advance- Bruce

You could try it with isp, and select a slower clock rate if the enviroment is too noisy for full speed or use rs232 or 485(a bit overkill) in between, tho I don't see why regular serial wouldn't work tho and just connect rx,tx and reset