Menthol pipe tobacco probably wont taste much like menthol. In a cigarette, the menthol is actually in the filter and not the tobacco, hence the flavour is so clear. With pipe tobacco it would be more of an aromatic than a flavour.
Not sure why myself. I figure if he enjoys it, more power to him. Some tastes in life can't be explained, like a friend of mine that likes sardine and peanutbutter sandwhiches or ketchup on his cornflakes...
I bought some Altaldis Frosty Mint around a year ago. The words "Frosty" and "Mint" being used in the title is not redundant. That's about as close to mentholated as I can figure. It even left my breath smelling minty for a few hours after smoking.
Not my cup of tea, but perhaps your friend would like it. It's good for inhaling as well.