theres no reason you couldn't build your own vtec controller.
there are only 4 things that the computer checks before activating vtec all you have to do is find out what's being sent to the computer and simulate it at the rpm you want (lie to the computer).
whether or not the person behind the ebay posts has done this and is selling the proper instructions is another thing.
P.S. im gunna get around to doing so eventually so... when i do i'll post the plans for free
also even if the plans are good and the unit works it almost definatly requires difficult soldering so... if you don't feel comfortable soldering then don't even bother.