The documentation I have read on several manufacturers of TGI's claim a round hole up to 1 1/2" can be made anywhere in the web as long as you stay 24" away from either end and provide 2 diameters (largest hole) of space between holes.
Larger holes must follow a chart that tells you how far from the center of the beam you can drill given the size of the hole you need.
I almost never hammer out the knockouts because they blow out bad on the backside and they never line up for a smooth pull.
The LVL's can be drilled too but with much less freedom. I prefer to go around those if I can.
Just looked up LP's chart and it's a bit different from the last one I referenced.
http://www.lpcorp.com/Literature/LP_SolidStart_LPI_18_Technical_Overview-US.pdf
