My Grill Block
I found it a little challenging to make a grill block that didn't look stupid with the stock grill. I picked up a cheap eBay grill that had a criss-cross pattern on it ("Civic Type R") that made it easy to mount the coroplast to. With the black coroplast and the black grill, it's almost invisible. Lower grill block was much easier to attach.
Both are just zip-tied in place and easy to remove in the summer and reinstall in winter. I leave the upper on year-round.