If you take out the slider, you can hold the vaporizer under the screened bottom board. Stand out of the way of fumes, though, and realize that they will not get the full dose when you do that. A better option is to cut a thin sheet of plywood to the same size as the slider, and put that in the lower slot. The vaporizer should then fit on top of that (depending on which one you have). Seal up the gap with duct tape, or masking tape, and you are good to go. You will need to do 3 treatments - one every 5 days. Be aware that the vaporizer will scorch the plywood - this is normal.
DO NOT put the vaporizer on top of the original slider - it will emit toxic fumes from the plastic slider, and will probably melt it too.