After the paint has dried for at least 24 hours, start cutting the wallpaper to fit the risers. Measure the size of the risers, measuring each one separately in case they vary in size. Use a framing square to make sure the wallpaper is straight. Use a utility knife along the edge of the framing square to cut the paper to size.
Test each piece of wallpaper on the designated riser before you paste it on. If necessary, use a utility knife, to cut off any excess. Set the piece aside but make sure you know which riser it belongs to; you may want to number the back of each one. Follow this process for each riser.
Follow the manufacturer's instructions for applying the wallpaper paste to the back of each piece. Place the wallpaper on the risers, smoothing out each piece as you go. Make sure the edges are secure. Use a damp rag to wipe off excess paste from the front of the wallpaper. Let dry.
Test the sealer on a piece of scrap wallpaper to make sure there are no adverse reactions. Apply the sealer to the wallpaper. Let dry then add two additional coats, allowing drying time in between coats.
Use white or clear painter's or silicone caulk to go around the edges of the wallpaper and along the stringer. Use your finger and lots of paper towels and a damp rag to remove excess caulk.