After way too much time wasted and general hacking around... I kind of / sort of figured out how to link from a Tableau dashboard to a Google calendar. I still cannot figure out how to jump directly to an "add new event" screen, which would be super cool! Their calendar API seems rather limited still, at least from a pure URL perspective.
At the heart of this example is the fact that I created a public google calendar and then tried to understand the possible variables I could insert into the URL. This part turned out to be rather undocumented, and it's quite possible that google will change this over time, thus breaking this example. If you download the workbook, you will see a Tableau "action" URL which includes the fields from the example data inside the URL.
I also had to create a calculated field called "stringy month" which pads the month integer with a zero for months 1 through 9, simply because google is apparently not smart enough to deal with this. Again, you can download the entire workbook shown below to see this all in action. It's easier to see than it is to type.
To begin: click on one of the heat map squares shown below. Each square is a month and a year. Hover over each one to see the date, total fictitious sales, and fictitious profit.