Hm that's not straightforward but also not so impossible. You'd have to write a wrapper that uses the Mac audio API and eventually ends up calling setup()/render(). To do this, it'd have to fill the BelaContext that is passed to setup()/render() with appropriate values coming from your audio API and whatever dummy values you want in there for digital / analog I/Os.
The simplest way to do these things - especially if they are audio-only - is to concentrate all your DSP code in a class method or function that is entirely Bela-independent, so that it becomes straightforward to integrate it in any system-specific audio callback. For instance, among the libraries EnvelopeDetector, Oscillator, Biquad, ADSR, among the Bela libraries, don't have any Bela API dependent code in there (if anything some have some ARM-specific code in the implementation, but that's beyond the point here).
