After spending hours looking for solutions that were purpose built for this kind of thing I gave up took PuTTYs source and made some tweaks to the UI.
The source was so easy to work with and I was so grateful that the license allowed me to do this.
The custom client only ran for a couple of years because the web replaced green screens. And being a *nix guy I don’t get much need for PuTTY in my day to day. But I’ll always be grateful for PuTTY for making that particular job possible (and secure).