Can I write a irule that uses a parameter in the url to specify the specific destination?

You could try something like this:

when CLIENT_ACCEPTED {
    set default_pool [LB::server pool]
}
when HTTP_REQUEST {
    if { [HTTP::uri] contains "?nodeselect=" } {
        set nodeselect [split [URI::query [HTTP::uri] nodeselect] "-"]
        pool $default_pool member [lindex $nodeselect 0] [lindex $nodeselect 1]
    }
}

This expects the desired pool member in a query string:

curl http://www.example.com/?nodeselect=10.70.0.1-80

This is a very simple implementation that doesn't address persistence or security. You may want to consider running this iRule on a separate VIP that's only accessible to the internal network.