I don't think you'll be able to use the Mendix cache bust value in this case, but I do think you can create your own. The answers on this SO article seem like a good idea - essentially a changing value (the current timestamp) every time you compile your SASS into CSS:
https://stackoverflow.com/questions/32840388/cache-busting-images-which-are-linked-inside-sass-files
So im not an expert on this, but I'd think that you'd do this through your compiling tool.
A lot of ppl use gulp to compile their sass and there must be a way to implement this in your build chain.
https://medium.com/@jasonteunissen/how-do-i-start-styling-in-mendix-gulp-sass-6b37ddaf8de6