To have the possibility to send an email exceptionnaly

I need to have the possibility to send the detail of on issue to a person at any moment, punctually.
Today, we are using the notification scheme to send an email on specific action.
But sometimes, we want to send the issue to a dedicated personn (not reporter, not assignee, not watchers), just to show him the issue or warn him of an action on the issue.

It can be a link "Send Email", after clicking on it, we can choose the receiver : single user, reporter, watchers, current assignee, project leader , group...