Hmm, I've put Class 1 Hidden Hitches on both of my Civics.  My 98 was
strictly bolt on but my 02 needed to have the holes in the frame widened to
pass the bolts.  I was a little wary of that step also but it REALLY was
pretty easy.  I got the cheesiest 10 dollar dremel from Harbor Freight and
ground the holes a little wider in just a few minutes.  Know that the extra
clearance you need is literally millimeters. I will also recommend the
hidden hitch, the quality is great and they are the most
unobtrusive/attractive hitch I found during my research.