Let's scrap boundary umpires and fill their role with field umpires.
Then reduce, from four to two, the number of 'non boundary' field umpires to two.
That will give us two running on the inside of the contest and four boundary umpires (now able to make free kick calls)on the outside of the contest. Hopefully improving positioning and therefore observation.
It would reduce the number of umpires on the ground by 2.
Reduce the the number required per game by 3 (one less emergency).
Would also give a larger pool of field umpires from which to choose.
Or we just wire up two umps in a corporate box at each end of the ground to radio missed calls to the on field umps.