Proxypass irule: match null URI separately from non-null URI

I want:

    "/" { "/location/program.jsp?1=2&a=b&x=y&foo=bar" }
    "/anythingelse" { "/anythingelse" }

but can't seem to match a null URI & query string - any ideas?

What I'm doing now is using RE's to match strings:

    "/a" { "=/(.*)=/${1}=" }
    "/b" { "=/(.*)=/${1}=" }
    "/" { "/location/program.jsp?etc=" }

but obviously this won't scale well.

Thanks.