I don't know how good a promotional technique this is, but here's something I've done.

I've sent a few complimentary copies to certain high-status individuals who either gave me permission for the use of certain things in my book or provided me with technical help and research. On the one hand, seeing their names acknowledged there and their "products" or whatever advertised in my book is free promotion and publicity for them. On the other hand, if they liked it and agreed to recommend my book to others they know, it's extra promotion for me, which in turn is extra publicity for them, since it is in their best interests.

As to how far it gets me remains to be seen, but it's still early days.