I don't think it causes a CEL. It will throw you a code though I think.
I didn't realize (or think about) just opening the throttle plate. I have a hand valve setup running to PCV inlet on mine which works just great, but I might have to try using the throttle instead. I will do tomorrow.
On a side note, the blockoff plate is incredibly easy to make. Just pull the IACV assembly off and map out the bolt holes on steel sheet metal. Then just cut whatever shape you want that covers the air holes, stick a rubber gasket sheet in between and bolt it on. I am planning to make an actual thick one out of an aluminum plate soon, but the sheet metal does do the trick.
The biggest PITA is getting the air regulator out I think. =)
Edit: Here's a pic of my current setup. Look up and right and you'll see the hand valve and line.