If you are not the kind of person for whom inventing artificial rewards works, you probably can do the opposite, leverage Pavlov and associate the cup of coffee to getting started.
Don't sip before getting started though!
For getting in the task, I've noticed doing a little superficial manual linting on a code works quite well for me to get inside it (I've recently inherited some non linted code). I guess doing some (semi) automatic, mindless task can help to get started.
For documentation, maybe doing some boilerplate labor could work. If you don't have rules to follow when working on documentation, maybe create some so you have a framework in which you can build habit.
Maybe having a checklist on what step to follow when writing doc would help too? Like "read the function, add the doc string, the description of the parameters, followed by the return values, etc.
Food for thoughts, untested, not a lawyer, not a physician, etc.