You cannot "T" off the loader lines. You will have identify the "Power Beyond" lines to the loader valve, and put a new valve that is set up for Power Beyond in series with the loader valve.
The other option is a Electric Diverter Valve, that will direct fliud flow to either the curl cuircit or the grapple. Either option will cost around $300.00-$350.00.
If you do a search on "Diverter Valve" you will find a number of posts dealing with instalation including my own I use for a snowplow and a grapple in the future. Be sure to set the "Date Range" to "All Posts", as it defaults to only one week.