The much-awaited(!??) calculator is here:
formatting link
The SPICE was easy; hard was writing, apparently half a kLOC of JS, just to graph the stupid thing...(Nope, no encryption or anything... ;-) )
But now that I've got that, I'll probably add fine-tuning adjustments so the user can manually fit it themselves.
And yes, that's a precision model of a Warburg element, four decade range. Feel free to use it, subject to the usual copyright limitations of course. :-)
Tim