The only way this can work in all honesty is if the files generated are not too big, otherwise its only going to be an option for people with masses of memory.
WHDLoad for the most part locks out the system, and as most people have enough memory for preload functions, thats the way it runs at its most optimum.
There is basic system functionality, but this is only on low mem machines where WHDLoad returns to the system to load files that couldn't be preloaded, but that wouldn't help as the game gets locked out whilst loading from the system.
The best thing to do would be to contact WEPL on here, as this is Bert Jahn, the author of WHDLoad, speak to him about your proposals, give him insight as to how the library works, a typical size for an audio file, and he will be the one to say yes or no.
The reason WHDLoad hasn't done it so far is because it would have to have a major fundamental change for something like this, and its simply not geared for it.
However, if the audio files were not huge, it may well be possible for it to run from preloaded RAM.
Speak to Bert