If you want to just look at the code in a GemStone/S image, and maybe try out a simple Smalltalk expression, you can spin up a Heroku dyno running GemStone/S. See the buildpack for instructions on how to run Webtools. Webtools is itself still quite rough, but if you want to contribute or open an issue, feel free.
Of course, this isn’t very useful as a database or application server because the dyno has an ephemeral file system and can be restarted any time. But it does demonstrate that I’ve figured out how to create a Heroku buildpack, and that was my primary goal!