The Constitution is silent as to the number of justices, Congress has determined how many supreme Court justices there will be. That number has been changed over time by Congress. Term limits are no different.
If the supreme Court wants to go that route, it is already been established that Congress can expand the number of justices. Congress can simply expand the number of justices, seat those justices, and then change the terms for Supreme Court justices with the new members voting in favor of the constitutionality of that change.
Even impeaching every Supreme Court Justice would be quicker and easier than the constitutional amendment. Congress unquestionably has the power to impeach Supreme Court justices.