I think that's about as close as you can get, and at least you could make an argument that there is no confusion as to source.
If you have a site that provides enchancements for users of another site, this might be a legitimate case.
But expect a challenge and expense in cases where the site is agressive about protecting their brand.
(There also were a slew of MacInFoo products. I think this gets into a much more grey area.)
It seems a real estate agent got a strongly worded letter (or a lawsuit, can't remember which) from Ebay because he had registered depoebay.com ... Depoe Bay is the name of a town in Oregon. So AFAIK this guy's case was thrown out, but it serves as a good example about how companies like Ebay take this very seriously.