Especially given that IW11 (10+ years) is so old, the only choice is to deploy your application as ISAPI and use the newer TLS options of IIS.
The only other way I can think of would be to use a proxy via IIS or other to tunnel to your existing application and provide the TLS via the tunnel.
The only other way I can think of would be to use a proxy via IIS or other to tunnel to your existing application and provide the TLS via the tunnel.