Dragging a header from the Solution Explorer into the editor is not an allowed operation. It would be nice if dropping "header.h" into "myOpenedFile.cpp" automatically added an include-statement for this header.
Are you aware of Add Include refactoring which is in the newer builds?
Finding anything in a comlex solution explorer tree can be slow. I'm wondering if it would be faster then using Add Include refactoring or just typing the header name (and the directory if applies).
Sure it wouldn't be faster than your current function. But... modern software often let you do the same thing using different commands - be it using the mouse or the keyboard.
It's just an improvement, not a replacement. Not to mention that gimmicks such as this tend to impress the user!