How to make conditional link via active_scaffold?

hi everybody!
Link to question on http://stackoverflow.com/q/31350221/2895006

As everybody usually says, I'm newbie in Ruby on Rails) and have
following issue:

I have a search form
https://www.dropbox.com/s/hmr85xh3ra28nsf/Screen%20Shot%202015-07-10%20at%2023.19.07.png?dl=0

and I would like to have ability to add new msisdn if it doesnt exist.
So I make fake insert and want to add conditional link to my
active_scaffold grid instead of currently exist ones:

config.action_links.add :submit_create, :label => "Create blacklisted
user", :type => :record, :confirm => "Are you sure?", :inline => true,
:method => :get
Here is my controller

class CCare::UserstatusController < ApplicationController

before_filter :filter_search

verify :method => :post,
        :only => :stop,
        :redirect_to => { :action => :index }

    > active_scaffold :users do |config|
    > config.label = "User Status"
    > config.list.columns = [:msisdn, :user_agent, :network ]
    > config.actions = [:search, :field_search, :list, :nested]
    > config.actions.swap :search, :field_search
    > config.field_search.columns = [:msisdn]
    > config.columns[:id].label = "ID"
    > config.columns[:id].search_sql = "users.id = ?"
    > config.columns[:id].search_ui = :text
    >
    > config.columns[:msisdn].search_sql = "users.msisdn = ?"
    > config.columns[:msisdn].search_ui = :text
    >
    > config.columns[:network].sort = {:sql => "network.network" }
    > config.columns[:network].search_sql = "network.network"
    > config.columns[:network].search_ui = :select
    > config.columns[:network].actions_for_association_links =
[:show]
    > config.columns[:user_agent].label = "Device"
    > config.nested.add_link("Subscriptions", [:user_service_list])
    > config.nested.add_link("Contact History", [:user_contact])
    > config.action_links.add "show_stop_all", :label => "Stop
All", :type > => :record, :crud_type => :create, :inline => true,
:position => :after
    > config.list.always_show_search = true
    > end

    > def update_table
    > if params[:search].nil? and params[:nested].nil?
    > render :partial => "shared/empty_list", :layout => false
    > else
    > if not params[:search][:id].nil? and not
params[:search][:id].empty? >and not params[:search][:id] =~ /^[0-9]+$/
    > flash[:error] = "ID is not a number"
    > render :partial => "shared/empty_list", :layout => false
    > return
    > end
    > if (is_msisdn_exist)
    > super
    > else
    > user = User.new
    > user.msisdn = params[:search][:msisdn]
    > user.user_list_id = 1
    > user.save
    > super
    > end
    > end
    > end
I tried to put method is_msisdn_exist into

active_scaffold :users do |config|
  ....
end
but it returned error: method not found. How can I implement my
conditional link?