A couple of the reflective materials like Panda Film, Ultra-flect, & Dureflect can be used to make a false wall by cutting a section (the size you need) & taping a stick to the top of the section & suspending it from the ceiling. If you have more than 1 side that needs reflective material but no wall to hang you could suspend reflective material or get insulation board and hang the reflective material from that. There are also a couple inexpensive indoor greenhouse available now like the Hydro Hut which has the reflective material built in.