Narrower wheels/tires?

Classic Prius used 175/65-14XL tires. In North America, only four tire models of that size with XL rating were available: Bridgestone Potenza RE92, Dunlop SP10, Nokian WR, and Barum Brillantis.

Standard load tires of that size were inadequate for the weight of the vehicle, but many Classic owners took a risk regardless, and used other tire models. Alternatively some owners moved up to a larger tire size such as 185/65-14 or 195/60-14, but this was discouraged by at least some Toyota dealers who warned of warranty issues.

Since 2G weighs more than Classic while its standard tire size is 185/65-15, this is probably the safe minimum from a load-bearing perspective, not even considering handling and braking.