redirecting urls to add www to the host if it does not exists

If your cert is only valid for www.sample.com, why not redirect all HTTP requests to https://www.sample.com?

when HTTP_REQUEST {
   HTTP::redirect "https://www.sample.com[HTTP::uri]"
}

Also, it's too late to bother with the HTTP hostname on the HTTPS VS as the client would have already gotten a mismatched cert warning by the time the HTTP traffic was parsed. It would be simplest to get a cert which is valid for www.sample.com and sample.com.

Else, if you have two separate certs for www.sample.com and sample.com you could use the new TLS SNI support in LTM to send the correct cert based on the server name indication in the SSL handshake. Note that some older browser don't support this though:

http://en.wikipedia.org/wiki/Server_Name_Indication

Aaron