How to alleviate the negative effects of using parallel LEDs with a common resistor?
Have R so big that the current wouldn't be too high even in case where only one led actually conducts. This prevents smoke-effects, but doesn't fix the possible non-uniform current distribution.

The leds  can all seem to illuminate acceptably, but do not expect it stay true when the parts get older or the temperature changes. If there's already a substantial brightness difference, you can try paint the brightest one slightly to make it dimmer.

My suggestion: Get a can opener and fix the circuit.