I know on the 20 series tractors, when a backhoe (NH) is installed, one of the three ports on the hyd. manifold is tapped into to supply constant flow to the hoe. This is done by removing the steel line to the valve and putting a hose with quick couplers in place of it. This would be at the power beyond port of the manifold. Your dealer should be able to point out which port it is. The purpose of the quick couplers is to make removal and installation of the attachment possible because it is not hard plumbed, (You would have long hoses from your splitter to hook up to the quick couplers). When hooking up the attachment, you uncouple the connections and plug in your splitter there by diverting flow from out of the loader control valve to the splitter control valve instead of back to sump. When removing the splitter, recouple the connections on the tractor and flow will be returned to normal. Hope this isn't too confusing.
The other alternative is to hook up to the rear remotes and bungee cord the control lever.