If spraying stuff inside works for you - great...
I've tried to spray all kind of stuff into air outlets and intakes and it worked only for a short time.. "Slam the Stink" method initially looks like it is complicated but it is not.
Drilling hole is simple - pic shows exactly where to do it. First, I drilled pilot hole with a largest drill I had (`3/8") and rest filed with regular round metal file to match plug size I bought.. My version of Sprayer is easier to make.. I bought a gallon size garden sprayer for ~$30 with brass spray wand and instead of soldering - using metal saw I made perpendicular cut on thick part - just behind the nozzle ( used to adjust spray) and just deep enough to cut through the metal - this way spray coming out makes like 180 deg pattern. To make is spray on the side instead of front -I unscrew the front nozzle and tape the outlet holes inside/under with piece of duct tape and put nozzle back so the front is covered and spray is only on the side...works great and you can really wash the evaporator .... >
That is the way BMW tool works - the only difference is that they cut the hole in plastic an install special fixture with sprayer depth control...