Sweet, you've been duped...kinda..
There is no way to add knock sensor functionality without a knock board. The P74/75 and P72 are the same mainboard, and the P74/75 are missing the vtec parts. There are spots for the parts, they just don't place them at the factory. It is very easy to convert to vtec and IAB starting with a P74/75 BUT without a knock board you've been mislead. I'm sure it probably has IAB and vtec functions, that's easy.

I hope you paid a decent price and got what you paid for, which should have been less $$ than a chipped P72.