If you are using chartjs for the second chart, you might be able to define a custom event listener on that chart and pass it a CustomEvent via dispatchEvent.
You could use that to transfer the necessary data from the main chart to the secondary chart. It would also bypass the round trip through the gateway.
Basic flow would be to add an item to the secondary chart's props.plugins with a definition for install that defines and attaches the event listener to the chart canvas. Most basic listener would look for new data in the event and shove that data into the data.datasets of the chart.
In your main chart's props.options.onClick definition, you would create a new CustomEvent that would contain the data you want to send, and maybe some other info to drive what the chart should do, and then pass this CustomEvent to the eventListener on the secondary chart.
Including this which shows basic creation and attaching of eventListeners: