Don't take the chance of contaminating your nectar by putting vegetable oil around the feeding portals. One solution is to add a few small feeders away from where people are likely to be bothered by bees. Birds will come right to your window. Sometimes it takes a while for them to overcome their initial reluctance, so be patient. Don't worry that a feeder on the window will cause birds to fly into the window.
Birds fly into the window because they see the reflection of the woods.
Window feeders and decals help break up the reflection. The red or pink coating is capstan, a fungicide used on seeds meant for planting. If you buy a bag of cracked corn or other seed treated with capstan, return it to the store. It can kill horses, other mammals and wild birds. I bought a bag of sunflower seeds early in the spring.