application of die da jiu
phantom,
There is really very little you can do to prevent the liquid from being absorbed by whichever body part you use. When treating an acute severe injury in it's earliest stages we sometimes need to be very careful about the amount of pressure we apply to the area. As I'm sure you can imagine we have much more sensetivity and control with our fingertips than with our knuckles. Basically I'm you don't need to worry about the absorbtion because it can't be avoided and that the fingertips allow for greater sensetivity.
As far as qi emission is concerned when stimulating the points I will have to give a big no on that one. Just think about snake stylists, ba gua practitioners, etc. Qi is strongly emitted from the hands in general but when trained properly can be emitted from any body part. The knuckles (like a pheonix eye fist) can be a nice way to apply very firm pressure to a specific point and I use them often when treating, but I also use my palms, fingers, elbows, knees, etc. As far as TCM is concerned the fingers (and toes) are a location where the transition of qi between the yin and yang paired channels. The qi is relatively superficial in the body and more easily influenced. Likewise it is more easy to emmit from there (think of the secret sword fingers in training the straight sword -gim/jian).
Anyhow, that's my $0.02
have a good weekend,
Justin