You could cover this in a number of ways.
One could be to have in your form a check box/radio button group that is approved/rejected (as you probably have at the moment) but also have a ‘forward to’
if they approve or reject the form routes as you have it already, but if they check ‘forward to’ then you don’t route to another stage.
if you set the conditions on your current routing rules so neither are using ‘always, if no other condition is met’ you can then have a behviour on your submit button (a standard button not a submit button in this instance) where you can set a rule based on the ‘if forwarded is checked’ that sends the notify to that required person followed by a submit data, and the ‘if forwarded is not checked’ that is just the submit data.
This will then mean that the form will follow your routing rules to the next stages if they do not select ‘forwarded’ but otherwise will send the notification and keep the form in that same stage
Hope it gives you a few ideas