When I developed the Alexa TTS integration for Hubitat, I also had an issue with a very long string (a cookie) that the user would supply. Due to the length limitation, I implemented it as a Parent App that created Child Devices. This works well because users often have multiple Amazon Echo devices. I simply let the Parent App handle all of the network communications since it can handle very long strings as a setting.
You can look at my code to see how I did it, although it sounds like you faced the same issue on ST already and may have a design that could be ported to Hubitat...
