Having read all the posts to this point--which contain many good ideas--it seems to me that a couple of solutions present themselves.

First, who said a knife must be carried in a front pocket? I've carried a large folder in my right rear pants pocket for about 28 years, and have rarely had it noticed. Currently, it's a Microtech SOCOM, which isn't a small knife by any means. I alternate with an Emerson Raven--slightly shorter blade, but OAL is about the same. Neither is clipped into the pocket, but carried tip down (my preference) along the outside edge. Normally, a bandana holds it in place, but in the past, with some larger than normal pockets, I have added a safety pin near the bottom of the pocket, thereby creating a miniature "pocket within a pocket" to hold the end of the folder.

I started to suggest boots, & some form of boot knife, but you indicated loafers were most common. Should you choose boots, though, you can clip a "tactical" into the top, or with a slight modification (akin to the loop in a pocket described elsewhere in this thread), just inside the boot, with equal facility.

Another option would be to carry the knife in your sock. Go to a "fine men's clothier" and get a pair (or two) of gentlemen's garters, like one used to see in old Bob Hope/Bing Crosby movies. They're made to hold up dress socks. They're elastic, encircle the leg just below the knee, and fasten to the sock with a garter snap. Adjust the garter to fit, attach it to the socks, and clip a lightweight folder, such as a Spyderco Delica, or maybe Endura, into the top of the sock. It's not exactly a Skean Dubh, and won't be fast access, but it will be with you.

I'll also second the Royal Robbins 5.11 pants. We're business casual, & nobody blinks at them.

Just my 2 cents...

David