As many others have mentioned, the serial console is the way to go. Even if there's no DB9/DB25 serial port out the back, there's likely at least one serial port header on the motherboard. The header/pinout is generally standard, so go digging in that 'really old parts' box that we all have and see if you can dig up a DB9 port mounted on a plate to mount where a card would normally go. It will have a ribbon cable to attach it to the motherboard...

This issue has been argued to death, but I feel I need to step in here. If you change an object's api in a dynamic language such as Ruby, you should have a solid unit test suite that will catch all the breaks. Statically typed languages let you typecast things to no end, so really they can quickly identify some problems based on type/method signatures, but completely miss others.