You certainly can, as long as you keep in mind the current limitations of the micro. Double check with Ohm's law, and the data sheets. Are the LED's turning on at the same time? What about a resistor network IC? One example I can think of is using one current limiting resistor for a couple leds, but the resistor is between ground and the leds. In my example, only one led is on at a time. Not the safest way to do things, but it will work. Proceed with caution.