@charliesome showed me an awesome little trick. You can force a ruby process to print out a stack trace. It's surprisingly simple to do.
Fist thing: find the process id:
$> ps aux | grep ruby
>> asellitt 36488 0.0 0.9 2625676 158132 s003 S+ 1:56pm 0:09.80 /path/to/ruby/proc/rails s
Once we have that, we can open up GDB and attach onto it:
$> gdb
gdb$> attach 36488
Once we've attached, we can call any function we want (provided its defined...) The function we want is rb_backtrace:
gdb$> p (void) rb_backtrace()
Quit gdb and flip to the tab containing the ruby process.
gdb$> quit
BAM!