The reason it's awkward is because etc. means “and other things”: et cetera. For your use, you need “or other things”, for which there is no Latin phrase in English (it would use vel, the Latin for or) and consequently no abbreviation.
This is a pity, because we are reduced to spelling out the alternatives. There's no handy three-letter doobry to use.
...where X is an A, B, C, D or some such.
You could use inter alia, “among others”, to indicate that other choices are available. You might get away with inter al. or even int. al., but it’s normally spelled in full.
...where X is an A, B, C or D, inter alia.