Adding a resistor to a battery pack? Answered

I am new to LED's and havent messed with electronics since the 80s, so excuse my ignorance and all of the questions.    My question is, if I have a 3 AAA battery holder, each battery is 1.5 volts, for a total of 4.5 volts.   If I have a 2 volt LED and use only 2 batteries (3 volts), can I solder the resistor into the 3rd battery compartment to lower the voltage, or must I use a dummy battery and put the resistor between the battery pack and the LED? 

Thanks!