Alternating LEDs with same forward voltage
If you don't need the left-hand LED to be completely off, just much dimmer than the second, you can try something like







simulate this circuit &ndash; Schematic created using CircuitLab

Assume the LEDs have a Vf of 2 volts. When the switch is closed, D1 is on with about 8 mA current, and D2 is off. With the switch is open, D1 is still on, but its current is about 0.6 mA, while D2 is on with a current of about 10 mA.