Did these instruction not help? How to enable a console user limited by scope to provision new devices that do not have a scope
Also I have you tried creating a query and creating a scope based on that query that has Computer.OS.Preboot OS or you can use Computer.Network.PXEBoot or if your scopes are based on network "Computer"."LANDesk Management"."Agent Configuration Name" NOT EXISTS AND "Computer"."Device ID" = "Unassigned" AND "Computer"."Inventory Server" = "Your Core server name" AND("Computer"."Network"."TCPIP"."Address" LIKE "Put in your Address Range" OR "Computer"."Network"."TCPIP"."Address" LIKE "Put in your Address Range")