Unfortunately, not yet. Analog channels are not available in the Low Level Analyzer SDK, so only digital waveforms can be processed by LLAs. The High Level Analyzer API does provide for analog measurements, but as far as I know you can’t get user customization of analog channels on ‘live’ waveform data stream (which only input from FrameV2 data coming from LLAs), per:
Also, even if you could get the analog channel data – the second issue would be how to display the FFT graphically. Right now, you can’t bind to a GUI framework within the native Saleae plug-in python environment without workaround for adding local extensions of the python environment (e.g., see: Third party libraries with HLAs - #2 by john).
Bottom line: I think there is limited analog channel support with ‘official’ APIs and SDKs at the moment. For now, Analog channel data is only available for text-based metrics on a user-selected ‘range’ of data (i.e., an analog measurement type of HLA that runs on a fixed time interval of one channel in a stopped capture).