This site caters to (and is run by) DPS-niks, it doesn't really take into account situations where a lower DPS move that can be fired off quickly is beneficial (e.g., where a 50-energy-use move attains a critical threshold like a KO more efficiently than a larger energy-use move).
That said, the statistic you wish to be displayed can be immediately inferred from everything else displayed. The "EPS" of a charge move is simply -100/# of bars.
The "EPS" or "Negative EPS" is otherwise not necessarily that useful as a presented number as nothing competes with energy once it is accumulated--energy solely exists to unleash the charge move.