I have ended up with a small collection of Heltec E-Ink displays and found that the official software hasn't quite met my needs. I figured that I might as well polish my code a bit and release it as a library in-case anyone else finds themselves looking for an alternative driver for Heltec panels.
If you think it could be useful, check it out at https://github.com/todd-herbert/heltec-eink-modules. It should probably also be in the Arduino Library Manager.
At this point in time it has support for:
2.13" Red V2
These seems like they are probably the most popular displays. I will probably add support for a few more at some point.
Hope that this all might save someone a few headaches in the future!