Something similar to this was posted to the HPV and WHIRL lists in 1996:

Coming (Eventually) to a Novel near You.....

I was tickled today to receive a reply to a letter I sent off a few days ago to an author of some popular light mystery books. I had gotten an idea to write to Lilian Jackson Braun some months back, and finally went ahead and did it, tracking down a home address through switchboard.com.

In my letter, I suggested that the main character in the series get 'bent, as mention was often made of the character's proclivity for bike riding. Anyway, her reply said "Your letter and suggestion of a 'bent for Qwilleran delighted me. I'm working on my 1998 book right now and can work it into the last chapter. Then in 1999 (if I live that long) Qwill can dazzle the locals as he bikes up __ Road."

"Since Qwill thinks best with his feet up, I'd say he's due for a recumbent bike. Thanks for suggesting it."

Then, I pretty much forgot about it.

...until one day in 1998 or 1999 when a package arrived. I was somewhat suspicious of the unexpected parcel, with a name and address on it which I didn't immediately recognize. But I began to think it sounded familiar, so I opened it - and what was it? A copy of the The Cat Who Sang for the Birds autographed by Ms. Braun.

I immediately started reading it to see where she talked about the 'bent. There was actually quite a bit about bikes fairly early on. From the description of one of them, it sounded like it might possibly be the 'bent, as it was a bike that attracted crowds and comments, but it just didn't seem quite right. (He has several different bikes.) Anyway, eventually the recumbent appeared late in the book, as the author had indicated in her note would be the case.

In the following book, there were some more recumbent mentions, but since then, three books total now, there has been no further sign of it....