Create specific resistances across a constant current source
You can use PN2222A NPN's as an approx 5 Ohm switch at this current level simulated here.  The switched voltage may not be identical but well within tolerance deviation for the LED Rs.  Although Rs is not found in datasheets, it occurs due to bulk resistance variations that affect Vf @ If variations.  Red is about 1.6V +If*10 Ohms @ 10mA and with a +50% tolerance worst case but +20% typ.
You may reduce the base resistors to lower the Rce effective value e.g. 220 Ohms.