What to do when electricity produces less carbon than gas?

Hello all, I'm working on a project for an owner who operates their own hydropower dam. It's an older facility and it the electricity it produces registers as basically carbon neutral. The owner has a strict carbon footprint reduction target, and so is actually much more focused on minimizing their natural gas usage since the electricity they consume is basically zero-carbon. If we optimize energy cost using standard utility rates we would actually increase the heating load in order to decrease peak cooling, but that will create a much bigger carbon footprint for this owner. I think a good solution to align the LEED energy score with the owner's carbon footprint goal would be to use a virtual electric rates based on the cost of electricity production at the dam (very low, even though they pay average costs for electricity at their meter) and purchased natural gas. Alternately, we could ask USGBC if we could use carbon reduction instead of energy cost savings as the metric, but I doubt they'd approve that. Anyone had a similar situation?