Interesting project @bradon! Given your intentions, I think that the Dynavox mouse emulation Software coupled with some kind of painting software that does not require the mouse click to be depressed may be the easiest approach. Ideally however, you would want a SDK project using a blank canvas combined with gaze location tracking.
I saw a project like this https://www.codeproject.com/Tips/811495/Simple-Paint-Application-in-Csharp may be able to combine with the Tobii Interaction Library API.