It's a challenging rhyme, yes indeedy But just rhyme on Pedy if need be. Though the homes that abound Are built underground It's opals that made Coober Pedy.
If you're unclear about the pronunciation just drop the Esses from "sCUBA sPEEDY". Coober Pedy is in the red earth outback of South Australia and claims to be the opal capital of the world. Because of its desert conditions and extreme heat in summer, many of its dwellings are underground dugouts with red clay walls. I visited the town once as a teenager and have been fascinated by the place ever since.
I've been thinking, Greg, but first I am confused about the pronunciation...and this may be a broader question. If you in Australia pronounce it CUBa PEEDy, is that how I should rhyme it? Because I am from the midwest U.S.A., I'd not change an "er" to an "a," as they do in the northeast U.S.A. and in England. I'd say CUBer PEEDy. Should I write it as people in Australia would say it?
Most people will just rhyme on PEDY anyway, but if you are going to take up the challenge to go beyond that, I don't think it matters. As in if you would normally pronounce the -ER as -A, you are going to do the same to any words you are rhyming it with, while if you pronounce it -ER then you are likely to pronounce the word you're rhyming with it the same way, so I think it will work for everybody whichever way you go.
In general we Aussies are a bit lazy and over here almost all words ending in -ER are pronounced -A.