Boards are not made BY HP, they are made FOR HP. HP will give the board manufacturer the list of cpu's they have secured for the boards,and this list will be decided by (some pratt that does not wish you to circumvent their pricing strategy) and a price list from the cpu manufacturer.
Check bios updates from HP, the i7 MAY have been included later. Dont be surprised if it was not,its an 8 thread cpu and the board may not be warranted(or even finished) to support 8 threads by the manufacturer. If you can find a custom bios in the HP forums you might do it that way.