I simply do this.
Use plastic envelope, wet out carbon with credit card, easy to see impreged, goes clear black and leaves close to good ratio, clean task if done right!
Use template for shape and cut with either razor knife on glass or sissors.
Peel one side of plastic and stick exactly where you want. If you want some better stick paint brush some epoxy on part and let set for a while until just tacky.
Able to apply hand pressure to position and adhere some to start, able to see due to clear plastic.
Can even leave half plastic envelope when vac sac pulled.
Warning, this is time consuming but as least for me works so well.
R H