It may not be that straightforward, but you might as well have a go. I use a standard JUCE widget for this which is created on the fly each time a users need to change the settings. It’s call in this function:
https://github.com/rorywalsh/cabbage/blob/master/Source/Audio/Graph/AudioGraph.cpp#L288
This function is in turn called from herre:
You can set the size of the settings dialogue here, but it might not affect the size of that child component. For that you may need to hack the JUCE source
Best of luck with this. I did create my own custom device selector for the last version of Cabbage, but it was a pain to maintain with all the changes constantly being made to the JUCE audio system.

