I've installed it and made my own for cars when I've replaced blower motors only. I think that I've even seen this piece of tape added to newer OEM blower motors but I'm not positive on that. I'm also not sure that I believe it's all that essential or worth the bother BUT if you want to do it, you can do it fairly easily yourself by removing the knee bolster, glove box and then blower motor. Once the blower motor is out you'll see the smaller hole in the lower left area where the blower motors "brush air" returns to the case, all that's done is that a piece of clear tape is added that blocks slighly more than 1/2 that hole and any tape will do, no need to buy anything that you can't find at home.
Note: the whole idea of this is really theory IMHO as I don't believe that there's any scientific evidence in print that proves the copper/aluminum corrosion idea. I've also replaced many evaps and have yet to see what I'd consider to be evidence of that occuring.