Is there a way to check if a virtual server exists from within an iRule?

We use virtual calls to deal with special needs for back end connections like NTLM or Server Side SSL on our main front vips. There are quite a few different combinations that we use to deal with these back end connections, and the switch statement that we've been using is starting to get a bit cumbersome. I was wondering if there was a way to do a lookup and see if a virtual exists rather than having to spell them out.

    when HTTP_REQUEST {
            set mapping [class match -value [string toupper [HTTP::uri]] starts_with SFNETSYSPERF01]
            switch $mapping {
                    "subvip1" -
                    "subvip2" - 
                    "subvip3" -
                    "subvip4" {
                            virtual $mapping
                    }
                    "" {
                            virtual subvip-default
                    }
                    default {
                            pool $mapping
                    }
            }
    }

What I'm looking for is a way to replace the switch with a lookup. I know this isn't correct code, but just looking to get the idea across.

    if virtual $mapping exists  { virtual &mapping }

Is something like that possible within an iRule?