Honestly, I don’t know I’ve only had one Arduino 2009 and one Rainbowduino to work with, so everything I’ve managed to understand was really grabbed from the 'net and then digested.
From what I read at http://arduino.cc/en/Main/ArduinoBoardUno (look for the paragraph Automatic Software Reset), it should be possible to disable the autoreset feature, I’d say that yes, you have chances.
As a matter of fact, reading on from the thread linked there, I’ve found this piece of advice:
If it really works on the Uno, I’d venture to say that you could use any Atmega 368 based Arduino as a real USB to serial converted by simply connecting RESET and 5V with a suitable resistor. To let the Rainbowduino enter flash mode, though, you won’t be able to use the RESET signal taken from the Arduino any more. Hence, you have to resort to the trick of pressing the Rainbowduino reset button a few seconds after starting the upload in the IDE.
Apologies to Miso for letting you into buying a converter befor attempting this one ;-(