Wind of Change...strumming question

Mathias plays a very cool method of strumming a double stop with a hammer on. You may recognize this method in songs such as "Wind cries Mary" by Jimi or Stevie Ray's "Lenny". It produces an awsome sound.

An example (not necessarily from Wind of Change):

E------------------------------------
B------------------------------------
G------------------9----------------
D------9----------9----------------
A------9----11---------------------
E------------------------------------

Play the first two notes together as a double stop and hammer onto the G# (5th string 11th fret) while letting the B (4th string 9th fret) continue to ring out. Then play the second double stop. In this particular example, feel free to hit an open E (6th string) immediately before playing.

Thanks bud!