The best way to do this, if you have to, is to group the LEDS in series in groups of N = 1, 2, 3, 4, etc, depending on the maximum supply voltage and the LED voltage drop, with N giving the maximum voltage drop that will work with your supply voltage. For example, let's say you have 2-volt red LEDs, and you are running them in a car, with a supply voltage between 12V and 15V more or less. You can make strings of 5 LEDs in series, giving a voltage drop of 10V, and to anticipate the maximum voltage at 20ma current put the string in series with a (15 - 10)/.020 = 250 or 220 ohm resistor.
You can them connect as many of these modules in parallel as you want. Of course as your supply voltage falls, the LEDs will dim. But they wont all blow up if one fails.
For decent results you need to "bin" the LEDs. Nowadays, the voltage drop from LEDs bought from the same source under the same part number will be within a tenth of a volt. But it's always good to test.