Install two sconces and one switch

run 12-2 w/g from your existing hot plug to the new switch. if only one wire is in this box add the new wire and attach it to the plug the same as the existing wire. if there are two wires already in the box you can splice all three together with a short jumper to the existing plug. all whites together. all blacks together, all grounds together. this makes everything hot and carries a hot wire to the switch. in the switchbox you will have the incoming line from the plug and a new wire to the first light. the black from each wire goes to the terminals on the single pole switch. tie the whites together as the nuetral is just passing through. tie the grounds together the same but add a jumper to the green screw on the switch. at the first light tie the respective colors to the light fixture and add a second wire heading to the second light. tie the respective colors together and you have it.