Apparently there are some "Red Bull "mini-dromes"" around, including some figure 8 tracks squeezed into small spaces.
I could imagine adding some creativity to the track venue.
Instead of building large one-time-use stadiums, they need to plan to use their existing resources. Perhaps it would be hard to maximize spectator access in small areas, but there have to be quite a few college, and even HS football/track stadiums within a few hundred miles of Boston that could host a temporary quarter mile open air velodrome.
Or, rather than doing a "Boston Olympics", do a country wide Olympics event, perhaps doing bicycling in one state, and running in another state, and kayaking in a third state.