I found this on the web:
Basically, this guy puts foam brush pads on the tips of salad tongs. You dip the tongs in concentrated roundup and then touch individual plants. I tried it and it's GREAT for getting rid of weeds among flowers or in the grass.
A couple caveats:
1) after each dip, squeeze the excess well so it doesn't drip.
2) Lightly touch the weeds at the base and wipe up. Stop b4 you get to the tip, or the plant can whip some drops onto the good grass.
3) Add foodcolor to the roundup to identify which weeds have been touched.
This thing was great for getting rid of quackgrass and ferns in my lawn.