We all know the rookie mistake of using LEDs in parallel and not giving them separate series resistors. They are often doing it for ill-founded incentives like "I want to save money on resistors", "I don't want to solder that much", and "They all have the same color anyway so why bother?".
The correct answer in such a situation is to persuade the OP to use separate resistors. Forums and QA sites (including this one) are full with such examples.
However, consider a case when it's completely impossible to avoid using a single resistor for separate parallel LEDs. I know it's bad. I know it's evil. But in a case it cannot be avoided, what methods are there to at least try to slightly alleviate the problems such a circuit
can will cause?
Consider a case with 2 to at most 5 LEDs of same color from the same production batch. The LEDs don't have to shine with their maximum brightness, so the current can be smaller than the maximum allowed current (although 1/x for the case of the device with x LEDs would probably be too low). The LEDs are inside a proverbial box, in parallel, and the box can not be changed. With the two wires hanging out from it, I can do whatever I want. Still, I would prefer simple solutions with few and only passive elements. (of course, complex microcontroller-driven solutions will also be appreciated, especially if no simpler solutions can be found)
Clarification: By "alleviate" I mean to reduce the brightness differences as much as possible, and, of course, to avoid them being damaged.