The problem with checking the plugs is , if you dont shut down the motor right after making a pull you will not see the detonation on the plug. You have to make a full throttle pull and as soon as you jump out of the throttle you need to kill the motor so it does not alter the plug in any form or fashion.
That is kinda hard to do on the highway. If yyou dont kill the motor asap and stop it from spinning it will alter what is on the plug and you wont find the fine bits of piston material that will be present otherwise.
He can check them now , but at best they will do nothing but show that , that cylinder is either running rich or lean based on appearance but will not reveal the particles that one would be looking for , for knock
Personally I would consider dumping that meth injection. Upping the injectors and run E85 for the fun stuff.
Get a tactrix cable and EcuFlash and get a 93 octane map so you can switch from lower boost 93 to a more of a kill mode 30 psi and E85 , hell I would run that E85 all day everyday.
Get a BR double pumper intank and some 1200cc injectors and tune E85