He did something pretty close early on: https://what-if.xkcd.com/4/

Upping the mass to the sun size would cause some interesting additional wrinkles because now we're talking about being large enough to have "problems" with the pressures in the middle being sufficient to start causing atoms to squish together, but it would take an astronomer to be clear on what happens next. My gut and layman's understanding says you might get a pretty big boom in a couple hundred thousand years or so, because you'd basically be building a sun that would be fairly far along its fuel consumption cycle.