That should be possible with 2 resistors and a series parallel circuit. The issue is that the leds take about 1.8 V (for red) to light and you only have 5 V to drive them. 4 in series needs around 8 V to drive them. Two in series (needing 3.6 V and a resistor to limit the current) in parallel with another two in series with a resistor will connect to a single Arduino port successfully as long as you don't draw too much current. The 100 ohm resistors in this circuit draw about 14 milliamps each with red leds which draws around 28 milliamps from the Arduino port which should be fine. The arduino port connects to the blue wire on the left end of the 2 100 ohm resistors and the top rail is 5V in this sketch.
series_paralel_leds.fzz (4.1 KB)
Peter