Buitenzorg has it right. No ppruner on earth has held a helo within 50 feet of reference while at 1000 feet, let alone higher, the visual cues are way too poor for that accuracy.
There are many survey systems that have a small DGPS transmitter that you set as a reference at a construction site, and then read the corrected GPS position within an inch or less.
Displayed on a crosshair X-Y plot on a laptop or handheld and you can easily hold reference if the winds stay steady.
Here are some examples:
http://www.trimble.com/geobeacon.shtml
http://www.trimble.com/geoxh.shtml