To hack together a working WakaTime under emacs on NixOS:
* Install both `wakatime` and `(emacsWithPackages [ wakatime-mode ])`
* Add the following to your initialisation file (default: ~/.emacs):
(custom-set-variables
;; ...
'(wakatime-api-key "XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX")
'(wakatime-cli-path "") ; sic
'(wakatime-python-bin "/path/to/profile/bin/wakatime")) ; sic
* `M-x global-wakatime-mode` to test your settings.