You can copy & paste an array of samples and Guesstimate will sample from that cluster. For instance, try pasting the following into the value field of a cell: [1,1,1,2,2,2,2,3,3,3,3,3,4,4,4,4,4,7,7,7,7]

You can use tools like distshaper6 to generate arbitrary distributions, then copy the samples into Guesstimate.

http://smpro.ca/pjs/distshaper/

Guesstimate doesn't yet support an input format for distributions outside of via samples.

I should add that I was thinking about this method -- Inverse Transform Sampling [1].

It's also just a fancy name for generating a pseudo-random number from a Uniform distribution in [0,1], and reading off the x-axis of the CDF.

[1] https://en.wikipedia.org/wiki/Inverse_transform_sampling