Amazing, exactly what I was looking for! I've had luck on http://carinthia.proxy.kiwisdr.com:8073/ (the link you posted seems busy right now)

I was able to use the FSK decoder, it worked really well. For those curious, the C-based decoder extensions are here [0]

[0] https://github.com/jks-prv/Beagle_SDR_GPS/tree/master/extens...